I thought it was great to come back and see a couple new spells in the game...so here is my idea for a new one.
This one could be learned as either an EO or an ED. Its called "reflect" and it would work something like this:
When cast as an EO any ED the other team casts your team will enjoy the benefit of. Any EO you cast on the team (except reflect of course) will also be cast on your team.
When cast as an ED, any EO the other team casts on your will also be cast on them, and any ED you cast on yourself (except reflect of course) will be cast on the enemy team as well.
I don't think it should dispel any levels for ED spells, since this would replace dispel magic. The spells still get cast at full strength, and both teams can enjoy the benefit of ED. For EO however, I think the reflected level should decrease the effects of current EO spells.
It could possibly work like AMF, where you would train some ratio of reflect:EO/ED to gain an effect. If both teams cast reflect (one as an EO and one as an ED) the level could just stack like an ED on multiple minions. Reflect does not protect against reflect.