Wow, I just had an incredible game on normal difficulty, we almost killed him in three rounds. A friend playing with randoms invited me when someone dropped out at the beginning. I suspect the other two players were partied up. We ended up as two teams of vampire flower and peashooter most of the time except when the fool appeared and during DPS time.
I'm FAR from a pro player, though I would classify myself and my friend as decently good players. I think it just requires four competent players who fully understand the game mechanics and are able to act together, and I think the fact that my friend and I were on mic must have contributed. As I said, I think from the way they were playing that the other two were partied up (likely with mics my friend and I couldn't hear). Germanshu on youtube has a video of a win up with only three players really contributing.
I think that, for better or worse, boss hunt is there more for giving experienced players a challenge and exclusive reward than for grinding rainbow stars. Even if things go well, it takes 20 minutes or more to earn 15 stars. The silver yeti crown looks like it was designed for commando corn. He might be a good choice for a DPS character, now that I think about it, except that peashooter and citron move so much faster.
I suspect that I've improved steadily as a player in the time since the Sasquatch hunt, so it's hard to compare, but so far I'd rank this as the second easiest boss hunt after the Gnomus Brothers, with Sasquatch in close running and Spooky Squash much harder. I never did get a win on that one (ironically, that was the only one I played with a pre-planned team that practiced together). But I've only tried it the one time, so I can't really claim much right to an opinion.