It all comes down to that pesky "intervening if" clause. In order for the ability to even trigger and go on the stack, it must be true at the beginning of the upkeep. From the official rule on gatherer:
The targeted player controlling more creatures than the current player is a part of the targeting requirement. A player can’t be targeted by this ability unless it’s true, and the ability will be countered on resolution if it’s no longer true at that time.
You can't manipulate the number such to influence whether or not it goes on the stack, but once it's on the stack (but hasn't resolved) you can.
From the Magic Judges Blog: (http://blogs.magicjudges.org/rulestips/2011/09/the-intervening-if[/)
If this additional condition is also true, then the ability will trigger and go on the stack. However this condition is checked again when the ability attempts to resolve. If this condition is not true at that point, then the ability will do nothing. In other words these triggers have two different times that they can ‘fail’ to do anything.
I meant to share this on the old TMD and never got around to it. I'm not sure how best to photograph it, being 100 cards and all, but here's my EDH deck.
I've been working on it for a while, starting out as a Rofellos deck, then switching to Omnath post-ban until I got the idea of just searching for Rofellos with Sisay :D. It's been through the bannings of Emrakul, Primeval Titan, Sundering Titan, Sylvan Primordial, and most recently Rofellos himself.
I've decided to make the deck as foil as possible, which is sometimes in contrast to my personal tastes (Sylvan Library and Loyal Retainers in particular, and to a lesser extent Sol Ring and Regrowth). Earliest possible foil printing on everything (though there are still a couple I've been lazy about updating from promos). I've been strict to these guidelines up until now, though the expedition Ancient Tomb is pretty darn tempting.
Even though it's a Sorcery, Forked Bolt is probably enough better than Dual Shot to consider the latter unplayable. The difference between Instant and Sorcery is largely mitigated by only costing one mana.
As per the OP, the werewolf reminds me a lot of this card:
While there are a ton of obvious differences, I imagine the majority of decks that would want to play the werewolf would want the Storyteller even more, and the Storyteller is basically unplayable. It's not a perfect comparison by any means, but the Storyteller seeing virtually no play is a good indication that this won't either. And as other have said, if you want to punish your opponent for interacting, the cards that prevent it altogether likely accomplish your goal even better.
So i bought a piece a little while back and just got around to framing it. I was going to share it on the Facebook group sometime soon, but then the shiny new TMD came along and figured this would be a good way to christen it.
Then, when uploading the new picture I realized I had taken a picture of it when I first got it, and thought it could be fun to see how others would have framed it. I'm not sure if anyone else will think this is an interesting exercise, but it's worth a shot.
So here it is: Meishin the Mind Cage from Saviors of Kamigawa by Thomas Gianni.