I don't have much use for coins in PvZ 2 but am still hungrily collecting keys in the Wild West world. When the Treasure Yeti shows up in the Wild West I'm happy to battle him in the hopes that his lunchbox will contain keys, not diamonds. But sometimes the Treasure Yeti appears in one of the two previous worlds, where I've already unlocked everything. Is there a way for me to make him go away (the sooner to reappear elsewhere) short of playing the level in question until the yeti shows up?
You can't skip the treasure yeti. Once it appears you either have to fight it or just let it run away. You can find more about the yeti here. You have to fully finish the level in order to continue.