Madness and such are overpowered, as it's basically the same as those "steal creature" cards, just without the part when it is moved to your side of field. It practically kills the usefulness of the creature to the enemy. No cost can justify it, or at least not 3.
Holy Water is reasonable, Holy Rain - less. It costs less than a basic Plague and can counter more than one Plague if your creatures withstand it. Also, it's situational, as not many things use creature poison. Just Death, practically, as Bloodsuckers are too weak.
Healer is very alright, Remedial would be if it kept 2/2 instead of a sudden bump to 2/5. Maxwell's Demon doesn't get 1-cost Paradox on upgrade, JUST the HP boost. Or whatever. I'd nerf the upgrade boost on this one, the concept is very alright.
Dawning and Sunrise both are nice things. Sunrise doesn't lose the boost, so it isn't situational, just gets a nice bonus against some decks. Of course, it's quite racist, as it specifically makes Black element weaker, but...
Amnesia is alright, but Immaterial creatures should stay untouchable. That's the very point. As for mutants/hatched, mutants should be returned to the state of the creature they're currently being, not the fodder, as you said, to make it programmable at all, as there is no history on what a creature has been.
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Memeento Mori, see above. Immaterial stay Immaterial, as you can't target an immaterial creature with any sort of unimmaterializing effect. It's like trying to tranquilize something with a slowdown mixture applied to an arrow when the thing is fast enough to dodge all the arrows. And it defeats the whole point of Immateriality anyway.