I love this wonderful old game and would love to see more conversation around it. And what better way to generate conversation than through controversial lists? So here's my ranking of the lower-tier summons.

Note: I'm excluding combat summons because they're effectively combat spells and fill a different role than overland summons, so comparing them seems odd. I've also excluded Floating Island because, again, it is functionally a very different beast than other summons.

So here they are, ranked from best to worst, IMHO of course.

1. Hell Hounds.

Hell Hounds have three major advantages: They're fast, they hit hard, and they're amazingly inexpensive. It takes a little practice to learn how to use them properly (i.e. making sure they have the initiative as often as possible to take advantage of their breath attack), but not a lot of practice, and once you've got it down you can easily overrun your continent with these guys. One of the biggest perks of going Chaos is the excellent early game Hell Hounds give you.

2. Ghouls.

Ghouls lack the speed and cost efficiency of Hell Hounds and being unable to heal isn't great, but their special ability more than makes up for it. Being able to turn your enemies into undead minions is just so key and will give you such a huge edge early on. They won't be able to overrun the continent as quickly or effectively as Hell Hounds, but any city they do overrun will come pre-equipped with a garrison ready to go, making it easier to hold new territory - or even send them out. The downside is that Ghouls really need Darkness to shine. Make sure to combo these guys with Black Sleep to nab higher tier units than what they could normally take, though beware the prohibitive upkeep costs for fantastic creatures.

3. Magic Spirit.

The Magic Spirit is more than just a node melder. Magic Spirits are dirt cheap, available right from turn 1, and able to move quickly over land and sea. They aren't particularly impressive in combat, but their ability to scout, explore ruins (and loot ones with little to no defense), and snipe poorly defended cities (and enemy settlers!), even on other continents, is huge, and makes these units a must in almost every game. They're also surprisingly durable, making them extra effective for wizards who have the option of using spells to do the heavy lifting in combat (like Confusion).

4. Sprites.

Sprites are tough to evaluate. As fast, flying glass cannons they tend to be either amazing or atrocious, without much in between. Unfortunately, even at their best, a base cost of 100 mana and 3 upkeep/turn is simply too expensive for what you get. In theory, conjuring up a stack of these can let you run rampant over your entire plane fairly quickly. In practice, you'd better have a truckload of mana and pray that no one has bowmen or shamans guarding their cities.

5. War Bears.

Have you ever looked at Hell Hounds and thought "Man, I wish I had something with half the damage output for twice the cost?" If so, then congratulations! War Bears are for you. They aren't terrible in their own right, but they aren't particularly impressive, either. They'll take down Swordsmen, Spearmen, and Bowmen pretty easily but will struggle against anything stronger. They actually trade pretty favourably with Hell Hounds if you can deny them the initiative - but saying "Hey there are certain situations where this unit can give as good as it gets against another unit half its price" isn't really a strong point. If you have literally nothing better to do with your mana, you could do worse than War Bears. I guess.

6. Skeletons.

Skeletons are very niche units. They're arguably the weakest summon, but are inarguably the cheapest one. They are uniquely suited to take down two units: Bowmen and Phantom Warriors. Unfortunately neither of those units are much of a threat anyway. The Missile Immunity on paper would make them good against Slingers - but they actually generally lose to Slingers in close combat, even with Darkness. Skeletons mostly serve as either emergency last-ditch defense or a cheap way of busting early Sorcery Nodes.

7. Guardian Spirit.

The Guardian Spirit has one niche and one niche only, and that's 11 book Life rushes. There the Guardian Spirit truly shines, and if you're looking to win as quickly as possible, it's the best summon in the game. But assuming you aren't doing an 11 book rush, it doesn't have a lot to recommend it. Stat wise it's identical to a Magic Spirit aside from having twice as much attack - which would be a point in its favour if its base cost wasn't almost triple the Magic Spirit.
One unit with 10 attack, 4 def, and 10 HP simply isn't as good as two units with 5 attack, 4 def, and 10 HP each - let alone three. The Guardian Spirit's main ability, being able to swat down other Spirits that try to meld with its node, is also pretty lame. The AI will swarm your node with Spirits and will win through eventually, which means you need to put defenders on the node to keep that from happening - which makes the Guardian Spirit's ability redundant. The one thing the Guardian does bring to the table is its ability to provide a stack-wide Resistance bonus - something that can occasionally be nice, but is rarely essential.

8. Nagas.

Nagas are a unit that could be really cool but just doesn't work out. First Strike can be really strong, but like Fire Breath it requires initiative, and Nagas only have one movement, meaning that's not always easy to get. Poison 4 is also potentially really cool, but most units have too high resistance for it to make much difference. Still, those things together - the opportunity to sometimes do 4 attack and 4 poison per figure before the enemy can retaliate - seem pretty cool, right? Well here's the kicker: Nagas cost 100 mana and 2 upkeep. That's nearly as much as Sprites, and you're getting way less. Nagas only have one saving grace, and that's their ability to swim - but if you want to launch an intercontinental assault, the 3 Magic Spirits you could get for that price will almost always be better.

Personally I think that Nature ends up being the loser here: While Life and Sorcery have the clunkers, those schools aren't about summons, anyway.

I also didn't factor in price discounts from books or retorts when looking at cost, because IMHO it remains relatively constant. Sure, Sprites look a lot more appealing with 10 Nature + Conjurer, but they still aren't going to be as appealing as 10C Conjurer Hell Hounds, or 10D Conjurer Ghouls.

Some of this looks okay, but only on paper. Some of it changes quite a bit when rubber meets road.

Magic spirits are terrible combatants. The only thing they are sniping are empty structures. They do make decent early scouts, though. The double strength of the Guardian Spirit means it is much more reliable about putting out some damage. I tend to agree about its meld ability, but keep in mind that swarms of AI magic spirits are NOT swarms of AI something else, and failed MS will give you a chance to get some more guards over to the node.

War Bears are okay, not great. You didn't note their contribution to possible pathfinding, since they have forestry.

Sprites are rather expensive, but they'll be able to roll over weaker units that can't fight back. Move in, blow through all your ammo, retreat, then rinse and repeat. Obviously they'll struggle against things that can fight back. They also have good mobility with the 2 move flying.

Naga are surprisingly effective in practice, between +1 to hit and 6 hp per figure. They also have the bonus that if you have Naga, you probably have Phantom Warriors, which means you have disposable shields for your naga.

I haven't used massed Ghouls yet (I should try that sometime), but massed Skeletons works out surprisingly well against weaker units. They don't have a great attack, but they've got a pretty good defense for their tier, and they are dirt cheap so who cares if you lose most of them winning a battle? The lack of healing is annoying, though.

Unit for unit Guardians do more damage, but mana for mana Magics do. The point is you can have nearly 3 Magics for every 1 Guardian, and the former will be stronger by a fair margin, and of course significantly more durable. Either way they can only take on low-tier units, and if I'm doing that then I'd rather have Magics over Guardians.

I will say that Magic Spirits are possibly the one instance where book/retort setup does matter, as their cost effectiveness becomes way less of a selling point the further you invest in one school.

re melding, that's a good point about making the AI focus their casting on Magic Spirits. The version makes a bit of a difference, here. Guardian Spirits are probably nicer in 1.31 where the AI is limited to casting only one spell per turn regardless of skill. In later versions where this is fixed, it's not quite as tempting. I agree on War Bears and thought my rating reflected that. War Bears are very middle of the road, with decent survivability but not much else. They're kind of disappointing in that way, because you'd think they'd be more like their namesake - solid offense and solid defense for a solid price. Instead it's mediocre offense and solid defense for a high price. I didn't mention their Forestry simply because there aren't all that many avenues for exploiting it, but you're right that it can be a perk if you're Dwarves or happen to land Baghtru or Brax.

Like you said, Sprites can be good, but it's a bit too difficult to predict whether they'll be useful and that makes them hard to build a strategy around. I think difficulty becomes a big factor here: On lower difficulties, where you are guaranteed a lossless retreat, Sprites are really, really strong. On higher difficulties, unless you're willing to savescum, you're liable to lose units every time you run away, potentially your whole army, if you're unlucky. If Sprites were cheaper that wouldn't be a big deal but at 100 mana and 3 upkeep a pop, that's a big deal.

IMHO Sprites aren't ranked 4 because they're mediocre; they're ranked 4 because they're simultaneously awesome and terrible and 4 seems like a good compromise. And that's the thing - if I'm playing on a lower difficulty where I can retreat with impunity, or if I get lucky and roll mostly cities or encounter sites that Sprites can roll over, then I'm going to dominate with them. But with Hell Hounds and Ghouls, there is no "if." There's no situation where they fail to thrive. Their one liability is an inability to cross water, which can be easily solved with a unit every race but one has access to (Trireme). Don't get me wrong, if you start on a small island that will certainly delay a Hell Hound or Ghoul rush and thereby reduce its effectiveness, but it's still very viable. For sure, and when you go up against Jafar, particularly on higher levels, you'll see that when you're facing endless hordes of them, Nagas can pose a reasonable threat. The problem is that 100 mana is absolute nonsense for what you're getting. It's not even remotely worthwhile. Mana isn't overly plentiful in the early turns in the game, but the real issue is skill. Skill is a huge limiting factor early on, and by the time you're able to squeeze out a Naga even once every three turns, you'll likely be able to pump out a Magic Spirit once a turn. And then, of course, once they're out the Magic Spirit moves overland twice as quickly. This is key because the earlier you can get to a city, the weaker its garrison will be.

So in a way, I think of Naga as "AI units." They're not terrible in the hands of a cheating AI with near-unlimited resources at its disposal, but in the hands of a player who has to ration their mana and spell points more carefully, they're almost never worth casting. I've tried this approach before and I find that Skeletons just don't do well enough against even Swordsmen to justify it. That may just be my own luck, though. Skeletons also run into the issue where they're competing against Ghouls for your skill points, and Ghouls will just almost always win - and since it's a common spell, Skeletons as a fallback in case you don't get Ghouls doesn't even matter because you'll almost always be able to pick Ghouls as a starting spell.

I will say that I think there's a definite argument to be made that I'm overvaluing Magic Spirits. A large part of their spot in 3 is because they're so reliable - they're effective scouts that you'll always be able to summon right from turn 1, can be surprisingly cost effective when massed, and their durability helps make sure you'll have enough turns to get out plenty of combat spells. But their effectiveness is definitely on a mana for mana level, not a unit for unit level.

I think you are vastly underestimating how much those extra swords per swing matter. I've tried using Magics in combat a few times, and they pretty universally come out on the losing end.

You might get a 3-for-1 deal on Magics, but low attack values will prevent the entire group of Magics from doing effective damage. Guardians will be able to push through armor much more reliably, which means they will take less damage overall as well.

I suppose I'll add "Magic Spirit swarm" to my list of things to try. Perhaps I haven't used them in large enough numbers. Sprites are expensive enough that you don't summon them en masse unless you have a target in mind. One or two can make decent scouts, if you can spare the mana, since they fly at speed two and have the flyer vision range.

When I spoke of Sprites retreating, I meant have them retreat by hitting the 50 turn limit. If the 50 turn limit is reached, all surviving attackers will retreat with zero chance of losses. If your sprites will be wiped out before 50 turns, then you shouldn't have attacked in the first place. I don't know if any of the mods have changed this. Naga are kind of pricey, but what else are you going to be spending that mana on if you are running Sorcery? The next permanent Sorcery summon is the rare 500 mana Storm Giant.

For scouting, sure get some Magic Spirits. For actual fighting? I'll take the 1 Naga over 3 Magic Spirits every single time. I'd guess that the main compelling cases for Skeletons over Ghouls are you either don't have Ghouls (1 book Death, found a book of Death, random starting spell selection) or you're anticipating Bowmen. Or you possibly just want massed fodder, where equivalent cost in skeletons have more hp and can split up. Magic Spirits ARE effective scouts, I'll give them that. I just think that for actual use in combat, they don't hold up. They have very poor stats for a single figure unit.

Just to try this out, I threw together a build that could quickly pump out magic spirits at 15 mana per unit using channeler and runemaster, and I sent them out to fight.

A pair of spirits were able to take down a single recruit barbarian swordsman, but both spirits took several hits of damage. I did hit and backup so the barbarian couldn't use thrown attacks. I sent a group of three spirits into a high man town guarded by 4 recruit swordsmen. Using swing-and-retreat tactics, they were able to take down 2 swords. Two of them were critically injured so I let them die in the process, and a third sword was easily able to cleanup the third spirit. I stopped trying at that point; it doesn't get much more basic than high man recruits.

Magic Spirits simply aren't effective combat units. They can scout and they can meld with nodes.

You forgot the real number one summon: Wraiths an I WIN button with an eleven death books start.
They fly 2, are incorporeal, so they cannot be crack called or webbed, are immune to normal weapons, no problem with towns filled with slingers the real threat at game start and being undead are also immune to illusions and psi blasts that enemy wizards throw at them.

The create undead ability will fill the just conquered town with a full garrison of zero cost zero maintenance soldiers in no time so you will easily conquer the arcane plane before your opponent begin using troops you cannot easily kill. You just need to attack opponent wizards the faster you can; ruins are just to recharge them if you happen to be hit by some spell. Forget about nodes, your target is the enemy fortress

I found it the easiest way to win the game, even easier than a full life myrran warlord start with halflings near adamantium

This in 1.31 impossible difficulty; havent tried in 1.40 or 1.50 yet

The list was about Common summons. Wraiths aren't included because they are a Rare summon.

My mistake, i interpreted 'common'ì as something many people do not the spell level

In the list are missing Chimeras and Basilisks, both stronger than all those listed, and Lycantrophy that is not techically a summon, you need a unit to convert, but in practice it is because the werewolves have a maintenance cost even if their casting cost is a bit of resources for a spearman and some mana.

Guardian Spirit should be higher in the standing; after you cast invulnerability it becomes very hard to kill and has enough punch to capture most neutral cities and some lairs.

Another 'rare' winning summon is Torin; with invulnerability and some unit enhancing life spells he's very strong even at low level and from level 3 he can self lionheart becoming near unstoppable.

Within each magic the spells are divided into 4 different rarities: Common, Uncommon, Rare, and Very Rare, with Common being the lowest and Very Rare being the highest. Higher rarity spells typically cost more to research, cost more to cast, and (generally) are more powerful.

Basilisks and Lycantrophy are both Uncommon spells, so one would expect them to be stronger than the Common spells like Naga. Torin is Rare, and that fact shows in how he can trounce even Basilisks and werewolves at fairly low experience levels.

Your point about Guardian Spirits is relevant (them being a Common spell). They don't really rate too highly on their own though, since it takes a rare spell to give them that power buff, and I think most of the other summons could do as well or possibly better with that same rare spell. Sprites and Magic Spirits are the big outliers for Invulnerability, considering their low melee stats.

Just gave a look at the viki; to be sure to be able to research all uncommon of a spell realm you need at least 8 books and only if you start with 11 books you are able to choose two uncommon spells and a rare one; with any book selection but the 11 of a kind you pick just common ones.

I played just a couple games from when i got again the game from GOG and a long time has passed from when i played it for very many hours on a 486, a really long time, too much to remember the details.

I remember some easily winning strategies: all life and halflings, invisible flying warships, wraiths at start and i can confirm they work even now with GOG patch, i also remember the many games i had to quit because of Ssra casting Armageddon before i was able to reach Myrror. Now i'm playing an 11 chaos early chimeras one that i remember as fairly easy, need to get back in touch before attempting my favourite: all death trolls