Feeblemind

Tips
Enemy necromancers in level 10 missions may cast feeblemind on you. Fortunately, they will target it on anyone, not only spellcasters, so some victims (such as barbarians) might be only minorly disabled. Having a 1 intelligence is less disruptive in DDO than in PnP, because only abilities which directly use intelligence or charisma are disabled. You can still communicate with PCs and NPCs, and remember which end of a sword to stick in monsters.

It is, however, a difficult spell to remove. Like Bestow Curse and Blindness, it is permanent and continues past deaths and logouts. Potions of Remove Curse and Lesser Restoration won't help, but there are other ways, which even level 3 characters can access (it doesn't require Heal, as the PnP version does)