Hey there. I'm making a Zelda-like right now and I managed to create a Knockback by using the BULLET function.
Unfortunately I cannot upload the CAPX as there are many other things in there I worked on.
Player On collision with [Object of Choice] >>> Set Bullet Speed to 400, Set bullet angle to [-angle of player and object]
Player Bullet Spd > 0 >>> Set Bullet Speed to [ (player bullet speed) - 1000*dt ]
You can just modify the dt multiplier and bullet speed to determine how much knockback you want.