For those of you considering Multitype, consider this:
1: If we use Multitype, and want to be able to counter any threat [Plausably], but not all at once, odds are, we'll need a decent STAB move for every single type. You're not going to counter Scizor as well without a Fire-type move, nor is Swampert going down without a Grass-type move.
And don't say it's not going to get a decent move of each type. That would defy the point of Multi-type, because some types would be 100% useless without a decent STAB. Don't get me started on Judgement either.
2: This gives CAP10 move coverage that isn't seen... outside of Mew, who's Uber. So, we'd be throwing the ability of an Uber, and a movepool of an Uber, onto the same pokemon.
3: Because the Multi-type CAP 10 could literally be anything, there is no way to prepare your team against it. As a result, especially with type coverage [And if we give this thing a useable attack, and speed stat, which we will need to do, to threaten stuff], this CAP will be difficult to counter in it's own right, nothing would be guarenteed to switch in safe.
Ability of an Uber + Movepoll of an Uber + No Way to prepare for it + No 100% counters... sounds like an Uber to me.
There are other ways to go about this CAP othr than slapping Multi-type on it. We just need to not tke the easy, and possibly broken, route.