Yes, the second dog (Black Wolf) is a fixed event, the player only have to run straight down to escape it. I should set a common event that gave hint when the player is caught/game over is it? Noted. The performance issue doesn't appear until the fourth dog for my case. If I can make this into a full game, I will separate the "one map" into (per challenge) several smaller ones to reducing the "just-too-many-events-in-a-single-map". I'm sorry for the poor grammar. Next time I will ask a native speaker.
Thanks for the inputs.