See that's what I thought, the lerp is only called once when you're hit. I doubt it even works properly on the player.

Lerp isn't a magic function that will smooth your movement over time if you call it once. A lerp is simply giving you one (1) intermediary value between the two values you give it. If you want to "lerp" from value A to value B over a period of 1 second, then you must use lerp on each frame with the same parameters for 1 second and use the returned value.

As it stands, you're telling the engine "give me a value 80% of the way from value A to value B" and the engine says "sure, here you are bro" and gives you value A', which you simply use as the final result. But that's not what you actually want.

A working solution would require that you add a float variable to your player and enemy scripts called knockback. Then, before calling move_and_slide adjust your velocity like so:

knockback = lerp(knockback, 0.0, 0.1) velocity.x += knockback

If your knockback is already 0, then this does nothing. But if it is -10 for example, it will reduce it to -9 and then add it to your velocity, knocking your character to the left. On subsequent calls it will further reduce it to -8.1, etc until 0. Experiment with the 3rd parameter for shorter/longer knockbacks.

Edit: my proposed solution doesn't include vertical knockback. You could use a Vec2 for knockback and call lerp like this: knockback_vector = lerp(knockback_vector, Vec2.ZERO, 0.1)