The second mode seems pretty pushed for a 4cmc instant, and the final mode seems weak by comparison with the other two. I get that they're meant to work together if you're playing four colors, but they still need to be balanced individually.

I haven't looked at any of the other contaminated cards, but I have to admit I find the flavor confusing on at least this one. If I contaminate this with Red or Blue I can destroy target creature while returning a creature from my graveyard to my hand? What about Red or Blue allowed me to do this?

Oh, right, credit where credit is due. I really like the keyword Contaminate. That's really strong. It just feels out of place here. I would expect to see contaminate do things like this:

­
Instant
Contaminate (If mana different from the card's colors is spent to cast this spell, it becomes contaminated.)
Target creature gets +2/+2 until end of turn. If ~ is contaminated, that creature gains flying until end of turn.

Personally, I don't understand the flavor of contaminate giving a bonus.

if you splash red/blue. It becomes "gain control of target creature"

This is however a very old card on my list of contaminated cards. I'll tweak it

Contamination is not "oh no the spell is contaminated it's bad".

It's more like " the spell has been corrupted by another color. It still works as it was intended, but it creates unintended consequences. "

Fracture is more "oops my spell broke and now it does different things."

With contamination, the power level is not linear. It's much easier to contaminate a mono-colored card than a three colored card. It makes sense that if a spell needs multiple colors, it's buffered against color contamination. That being said, the spells that do get contaminated are the ones with contaminants that are very strong. This is why 3 colored contaminated spells have stronger effect.

1WBG gives destruction/reanimation/speed

The Mastery cycle is supposed to be like the Command Cycles for this set. They're supposed to be strong, pushed and pushes people to play four/five colors. They're supposed to do something for each then if four color is used, doing something unintended for what WGB is supposed to have. This was supposed to be a Ray of Command if contaminated.

Ah, I see. I just made the assumption that you'd almost always use your graveyard, since you probably will. If that's the case, I'd suggest making the second ability Ashen Powder instead of Rise from the Grave. I'd say something about it being odd that blue mana gives a creature haste and intimidate... but maybe I should just stop poking the bear.

Well, green is tertiary in haste, and you do need green mana to cast this. I don't think green can actually grant haste, though.

black gives haste and intimidate