|It increases the power of its wearer's magical spells.|
This ego is useful to help maximize spellpower, although it serves no purpose on spells where you have already reached your spellpower cap. Additionally, spellpower is calculated on a diminishing-returns basis; hence, if you already have very high spellpower, Archmagi will grant less than it would on top of a lower spellpower.
The spell enhancing effects of Archmagi are particularly useful for binary schools of magic, such as Hexes. Conjurers and other direct damage dealers might simply deal a little more damage per hit, but for Enchanters, this ego can make the difference between the spell succeeding or failing entirely.
The archmagi ego can be found on:
In ancient versions of Crawl, before 0.8, this ego reduced spell failure rates in addition to increasing spell power, but it also reduced XP gain to 1/4 of normal, providing a serious threat of undertraining to most characters.