Note: Although this exploit can be used on all the items you can make, I've found it is best to use only on a heroes weapon. {When a hero has two or more items using this exploit, sometimes none, or only one, of the choices is available and it may not be the one you want.}

The Exploit:
1. Design a staff with Spell Charges (Flame StikeX4, WebX4, HealingX4, et al).
2. Make sure the staff mimics the actual weapon you want to create (EG an axe can only have a +2 To Hit while a Staff allows for +3, so choose +2 To Hit if you're making an axe).
3. After you have chosen your four abilities, turn off Spell Charges, and pick a different fourth ability.
4. After you have chosen your replacement fourth ability, switch the staff to the actual weapon you want and 'create' it.

When your new weapon is made, it will have the four abilities you chose, PLUS it will have the Spell you chose.
This exploit does not increase the value of, nor the mana received for destroying, the artifact. But it will have 5 abilities instead of the 4 max the game claims is possible.

PS: I don't come to this forum very often, but if you pose a question in this thread, I (or someone else) will eventually respond.

To be more precise, the game only ever checks Spell Charges on weapons. While they may show up when inspecting the item if bugged onto an armor or miscellaneous item, they won't ever work from there. This also means that unless you hack or mod the game, you can never have more than one item spell available at a time on a hero, because they all have only a single weapon equip slot.

I wonder why you picked this particular exploit to post about when there are much more game-breaking ones, and this is pretty well documented already.

Acquire Runemaster + Artificier. The discounts stackk, allowing you to craft weapons for less mana than you get by breaking them. You can spend your casting skill generating mana from basically nothing.

This was already included in the BJacobson / DSimpson faq (dating back to '95 / '99), and is described in some detail in the wiki article on Spell Charges as well (masterofmagic.fandom.com/wiki/Spell_Charges_(Item_Power)#Known_Bugs, for some reason this isn't accepted as a link o.O).

As for other exploits, there are just way too many in vanilla 1.31. Arguably the most powerful though, is this one. I'd urge anyone not strictly interested in this to not click the link. It's an awful spoiler. Close second though, is the mana overflow bug that doesn't allow casting spells during fortress defense if one has over 16,384. That works wonders against Impossible Sss'ra, especially since the victor also gets half of the loser's mana after the battle...

Mind you, these are all the results of bugs (as opposed to what Bookwyrm627 mentioned, which is by design), and as such won't work any more in the Community Patch (including the Spell Charges exploits).

I always felt this was more a perk than an exploit... it requires two slots one of which is pretty poor in other ways, and requires the Wizards to use their casting time creating items instead of doing other overworld spells. But I admit I've never really used it as its so boring, so maybe it's far more powerful than I realize. Others also play at a much higher level than I do, so maybe the advantage shines there.

I think the most powerful exploit in vanilla 1.31 is the ability, as defender, to occupy a square that can't be attacked. Especially exploity with a ranged unit of course, or combined with a damage-over-time spell like Wrack. It's terrible, though I admit to occasionally using it to get out of a tight spot back then.

Another defensive exploit is the ability to prevent an imminent AI attack by some huge stack next to your city by attacking them first... a single spearman attacking and retreating prevents the stack from attacking for one turn. At least, I think that was 1.31, it's been a while.

That's correct, and it's also a bug.

It lets you ignore mana generation early on, giving you more time to both research spells and grow your casting skill. The latter is especially important (at least for me) because skill is what determines how much mana you can use per turn, as well as in combat. And it takes F O R E V E R to grow, especially early on.

But once my spell skill is high enough, I can use it to pump the best units out of one or more specially dedicated military cities, and (via multiple uses of Summoning Circle and Word of Recall) deploy them wherever they're most needed that same turn.

Even better is the feeling of being able to cast the Spell of Mastery in three turns or less. Muahahaha!

One of the really nice parts here is the loop that is created. Spending mana to create artifacts to break for mana frees up Power to use on Skill, which allows you to spend mana faster to create more mana which keeps Power free for Skill. It also fuels the costs of casting spells in battle, which can help you take some fights earlier than you'd otherwise be able to.

Also, you can deck a new hero out almost immediately. Nice side perk. :D