It's a crazy idea, and I'm still trying to think of ways to refine it. If you have any suggestions for the "build up/win condition" planeswalker, I'd love to hear them!

Hmm... I'd normally rather have Darksteel Reactor. This can be attacked.

But more generally - isn't this what almost all planeswalkers are like? The middle ability is fairly tempting, occasionally necessary, but if you ignore the middle ability (or look at double-plus planeswalkers like Elspeth, Knight-Errant or Nissa Revane), the pattern is "Plus for a minor effect, plus for a minor effect, plus for a minor effect... woo, finally got there! Minus for the big stompy ultimate!" (Elspeth's ultimate isn't so clearly "win the game", but Nissa's, like most planeswalkers e.g. Sarkhan Vol or Jace, the Mind Sculptor, really are "better have an answer right now or I've won".)

Dang it! Whenever I think up a card, it seems WOTC has thought of it already. Oh well.

Welll.. there IS value in a flat "You win" statement. It's exceptionally splashy, and that's where planeswalkers and mythics dwell.

I'd say get rid of the reminder text; and work out how small you can go. -50 is clearly "You have to be using doubling season and proliferate and even then... maybe?" Can you go as low as -8? Can the casting cost be lower, so that people go for this as a 1-drop and then desperately try to protect it?

So yeah. Planeswalkers can do it. Darksteel reactor says yhou can be more aggressive; and the planeswalkers vulnerability says you can go even MORE agressive.

I'd honestly try this as and -10 for a first attempt. Might need to make it weaker than that, but go for it.

Hell, if he's gonna be mythic, go bigger and better.

CMC:3

Loyalty:1

+1: Proliferate.

0: Choose a player or permanent. Give that player a counter of any type of your choice.

-3: Double the number of counters on target permanent or player.

-10: Remove all counters from target permanent or player.

-20: You win the game.

Yes they could fit this many abilities on a card, the text actually takes up very little space, plus they can change the frame as with Jace, plus reduce the font size if necessary.

Put a -20/-20 counter on your best creature (even Progenitus) every turn, for ? I'd have it.