­Planeswalker's Scorn + Moldy Rock

Keeps the "Big effect, big drawback" of moldy, and the scorn turns it into a creature killer and a planeswalker.

So; a somewhat terrifying murder stick; with a vast drawback. Reasonable?

Hmm. Tough to call. That seems like a strong drawback, but in many control decks, it roughly replaces your next draw, with drawing a card named Murder and casting it for free right now. Sure you don't attack with your creatures, but 'draw-go' doesn't do that until much later in the game. You also don't get to untap... but you don't need to untap if you aren't casting counterspells... and you aren't casting counterspells because you're casting Murder instead.

But... hmm... I guess you're only able to cast Murder every other turn. Don't know. It is tough to price...

That is really interesting. I really can't tell whether it's unplayable junk or a regular part of tournament decks. (Either way I think the mana cost is about right.) Nice work.

I suspect just on pure card advantage (This will always remove at least one card from an opponent, and usually at least two as they kill it) it's too strong.

But you're giving up a draw step (one card) each time you kill a creature (one card).

Mmm, true. And almost all the tricksy ways round getting your draw without a drawstep won't work either; as you don't get an untap or an upkeep either. Unwinding Clock and (I dunno, Candles of Leng and some mana artifacts) is the only way round it I can think of offhand.