Somewhat inspired by Timesifter. Could refer to least power instead of most power. Not sure which would be better. That would make it more like an insane version of Drop of Honey/Porphyry Nodes.

Ooh, that's very entertaining. It feels fair in that I lose my biggest creature but get another turn. The flaw I see is that if the opponent doesn't have any creatures on turn three (which is not too unlikely) this is likely to lead to a permanent lock...? Perhaps require the creature to have lost summoning sickness, or choose any 5+ power creature at random?

It only makes a permanent lock for as long as there are creatures on the board. If you draw a creature every turn, then sure. But you'll likely run out eventually. Then it stops granting extra turns and sits around waiting for someone to play a new creature.

True, but even three or four turns would be a giant advantage, and if you fill your deck with cards like Khalni Garden, Myr Sire, Mogg War Marshal and Kher Keep ETA: Reassembling Skeleton. Maybe that's sufficiently Johnnie to not be a problem, or maybe playing it when your opponent doesn't have creatures is sufficiently hard, (and it may be ok in limited/block constructed) but it just tripped my "watch this carefully" alarm.

I can try to build a test deck for it if you like :)

You also have to ask what happens when you run out of creatures. As you say, this sits around until another one appears, which it promptly offs. Unless you can repeatedly play more than 1 creature per turn, it'll be very hard to win through normal damage.

­Drop of Honey eventually killed itself.

I feel like this should be a Mythic Rare, but maybe that's just me.