Mega Blastoise
Yeah, it's a bit overrated in some respects, but I think it's the better pick here. More significant in how the tier became what it is than any one mon you can nominate, and while it wasn't the face of a dominant playstyle like Sharpedo was, there's a lot to support it. It was a boon to so many builds, a deciding factor in the viability of the opposing hazards game on top of something that was actually really hard to figure out how to check it for a while makes it worthy here.