DarrkPhoenix: Army choice is quite important for this battle. Archers/elves/hunters aren't particularly useful as skeletons and bone dragons have a very high resistance to arrow attacks. On the other hand, priests/inquisitors are quite good ranged units to bring along, as they get a damage bonus against undead. Black dragons are also a good choice as their high magic resistance means you can park them next to necromancers and they can trade blows while taking very little damage (as necromancers do magic damage); depending on positioning you can also use their opening move to fly while breathing fire, damaging several enemies, parking them next to a stack of necromancers, and also creating a hole in the barrier for your other units to move through. Lake faeries or sprites are great damage dealers (with no retaliation), and if you're using Anga's Ruby will be very fast and have high critical hit rates; a tactic to use here is get a stack of them right in the middle of the enemy to draw most of the first round attacks, then use Time Back to undo all that damage at the start of the second round.

For tactics, you need to be fairly aggressive in this fight, so that you can take out the enemies faster than Karador and the crystal can raise them. Don't focus on taking out the crystal until the end, when you've pretty much got the rest of the battlefield under control. Focus your initial efforts on taking out any bone dragons on the field (as they can otherwise be quite a pain), along with any massive stacks of skeleton archers (priest/inquisitors can take these down pretty quick). Neutralize any necromancers by parking some black dragons next to them, but don't worry about focusing much damage on them initially (as they take a while to kill, and your efforts are better focused on quickly killing other enemies). If vampires are present try to wait for them to shift into bat form before attacking them, as they have fewer HP in that form (plus any ancient vampires, in vampire form, automatically dodge any critical hits). For any big stacks of slower units (skeletons, zombies, black knights, undead spiders) try to just control them with things like slow, traps, and Ice Thorns while you take out the more mobile units and ranged units.

DarrkPhoenix: Army choice is quite important for this battle. Archers/elves/hunters aren't particularly useful as skeletons and bone dragons have a very high resistance to arrow attacks. On the other hand, priests/inquisitors are quite good ranged units to bring along, as they get a damage bonus against undead. Black dragons are also a good choice as their high magic resistance means you can park them next to necromancers and they can trade blows while taking very little damage (as necromancers do magic damage); depending on positioning you can also use their opening move to fly while breathing fire, damaging several enemies, parking them next to a stack of necromancers, and also creating a hole in the barrier for your other units to move through. Lake faeries or sprites are great damage dealers (with no retaliation), and if you're using Anga's Ruby will be very fast and have high critical hit rates; a tactic to use here is get a stack of them right in the middle of the enemy to draw most of the first round attacks, then use Time Back to undo all that damage at the start of the second round.

For tactics, you need to be fairly aggressive in this fight, so that you can take out the enemies faster than Karador and the crystal can raise them. Don't focus on taking out the crystal until the end, when you've pretty much got the rest of the battlefield under control. Focus your initial efforts on taking out any bone dragons on the field (as they can otherwise be quite a pain), along with any massive stacks of skeleton archers (priest/inquisitors can take these down pretty quick). Neutralize any necromancers by parking some black dragons next to them, but don't worry about focusing much damage on them initially (as they take a while to kill, and your efforts are better focused on quickly killing other enemies). If vampires are present try to wait for them to shift into bat form before attacking them, as they have fewer HP in that form (plus any ancient vampires, in vampire form, automatically dodge any critical hits). For any big stacks of slower units (skeletons, zombies, black knights, undead spiders) try to just control them with things like slow, traps, and Ice Thorns while you take out the more mobile units and ranged units.

DarrkPhoenix: I assume you're talking about not having room to buy the Resurrection scroll, as there's no limit on the number of learned spells you can have. There's a limit on the number of scrolls you can carry (shown as a number like 34(23) right beneath your mana when you open your spellbook). The limit on scrolls doesn't prevent you from picking up additional scrolls that you find, but it does prevent you from buying additional scrolls if you're over the limit. The simple solution is to just sell any excess scrolls for spells that you don't need (which will also net you some extra money) until you're under the limit (if you don't know how to sell scrolls just open up your spellbook while you're visiting a castle, then right-click on the spell scroll you wish to sell).

Also, a few tips for Demonia. First, any units that do fire damage (such as red or black dragons) are not very useful, as all demon units have a high resistance to fire damage. Green Dragons, though, can be quite useful, as they have a high fire resistance, do straight physical damage, and one of their abilities can recharge a fair bit of your mana while damaging every adjacent enemy. Also, the spell Magic Shackles (preferably at level 3) is incredibly useful, as it will prevent demon units from using some of their more annoying abilities (such as the imps throwing fireballs, or succubuses using Infernal Exchange). Level 3 Magic Shackles takes a whopping 40 mana to cast, but in many battles it's really worth it. You'll also be facing a fair number of high-defense, high mobility, level 5 units (namely red and black dragons, and arch demons); a good trick to taking these down quickly is bring along some Hunters, then using Dragon Arrows (preferably level 3) on them. Dragon Arrows ignore all defense and resistance, so will allow you to do much more damage than normal to high-defense units. Pair them with the Dragon Slayer sword (gained after winning the final fight in the tournament in Darion, although it can also sometimes just be bought) and you can take down dragons extremely fast. There's also a weapon you can acquire in Demonia, the Sword of Kerrus (+3 Atk, +3 Int, +30% damage to demons) which you should definitely get before trying to take on either of the two bosses there. Finally, watch out for the volcanoes in the fire terrain- if one of your units is within two hexes of them they'll cast either fireball or fire rain on them, doing some pretty big damage (2000+); keep your units clear or destroy the volcanoes.