I like the Idea a lot ... Good Job!
What about 
Flood and 
Nightfall ?
I think flood would work as it should, and nightfall... +1(2) to weapon if the owner's got a vamp dagger equipped 
It only works for spells. "Target creature reflects spell effects back to the spell user." Nightfall and Flooding are permanents.
I was joking about the nightfall thing, hence the "
"
what happen if you use mutation on creature that already have this status and your weapon already have immaterial?
If it's going to work like flying weapon or voodoo doll (targeting the slot, not the weapon itself) then it'll still mutate, otherwise... who knows?
