[quote=@Eklispe]
The only card i've seen seems cool, though does seem like you could simply have them use spell counters instead of mana counters. Of course i'm not sure how many other monsters use mana counters.
[/quote]

Spellswords are the only monsters with Mana counters. Spell counters were to broad of a category to me, plus the spellcard "Spellsword Strike" places a Mana Counter on a single monster and makes that monster loose 200 atk for each mana counter on it.