In mulligan, you want to always keep Witchwood Grizzly. You should also go for weapons and removals, and if you don't have a Grizzly, Tracking and Stitched Tracker should also be kept.

Your primary game plan is to drop a Witchwood Grizzly on turn 5, and then start your shenanigans with Carnivorous Cube(s) and Play Dead. Surprisingly many decks can't handle more than five Grizzlies, so if you manage to reach this point you've won. This can also wait a few turns, and Amani War Bear can occasionally work as a substitute for the Grizzly, but any later than that and it's probably too late. Play Dead can also be spent on an Abominable Bowman or Kathrena Winterwisp.

However, there are some off-the-wall border line meme decks that challenge this one in greediness. If you happen to run into one of those, you must not waste the Cubes on Grizzlies, but save them for Abominable Bowmans and Kathrena Winterwisp.