That ability can be a bit awkward, because its so reliant on your opponent having a big creature in play, but there are a number of things you can do to get maximum value out of Dong Zhou
White and blue are both very orderly colors
When it or more Warriors swing you can make their dork a Coward
If I have access to the best mana rocks for my Commander deck, I should usually prioritize those over any situational ramp spells, but use my best judgment when comparing them against my best mana ramp options
The payoff of transforming to Aang, Master of Elements is massive considering you already drew 5 cards (assuming you drew a card to start your turn)
Still very powerful most of the time, and even if you dont have a land to ramp into, you usually still walk away with an extra card