"Counter the next spell cast before your turn begins" perhaps? Not only does the +1 have memory issues, but it's a brutal thing to just have hovering over your opponent... especially since you don't have to cast spells and can sit there, activating your Planeswalker every turn...

Also, I don't know if it stacks with itself. I'd think that if you activated that ability 3 times that it will only counter "the next spell" and remove all 3 iterations. That isn't how "skip your next turn" works, though... each iteration of that effect makes you skip multiple turns. So it is possible that you could keep using this to dig a gigantic hole for your opponent.

You can no longer activate it each turn. Even if you did, it limits you as well. It also prevents you from transforming it.

Is this a subtle prod to make me implement transform cards quicker? :P

I suggest the day-side minus-2 ability should read "The next time a player casts a spell, counter it." That'll clarify that yes, if you activate it 4 times, all 4 will trigger on the same spell, you don't get to save them up.

This is a very pleasing design, though. The -6 isn't very much of an ultimate; at the moment this looks more like a 4-cost 'walker than a 5-cost one.