Here are some ideas I had about what active skills some of these mages could have to fit with the theme:
(Quite powerfull indeed, the ability cost should prob be at least as high as nymph's)
Priest

: Redemption: all negative effects are removed from the target creature (Freeze/Poison)
Oracle

: Vision: The next card in your deck and in your opponent's deck are revealed to you until next turn.
Archmage

Magic Wind: deal 1 dmg to each of your opponent's creatures.
Invoker

: Abyss Summoning: create an Abomination or a Spark.
Necromancer

: Revive: Create a skeleton, at least one creature must have died on this turn or your opponent's last turn