“Why not activate its ability after you turn it face up?” Great question. Even though turning a creature face-up does not use the stack, and you retain priority after it’s turned face up, state based actions are actually checked after it turns face up, before you get priority. When this check happens, you have a creature with 0 toughness and as a result, your Hangarback goes to the ‘yard before you, or anyone else, can do anything about it.
If you are adamant about keeping your Walker, you may want to put some +1/+1 counters on it while it is face down. This would better ensure your Walker lives and gets you the value that you deserve!
Today’s Rules Tip written by Daniel Clarke