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Shaders are pure magic created by math wizards :D
I used this one to make the hit animations with some minor modifications https://godotshaders.com/shader/color-cycling-hit-effect/
This Video explains how to add shaders in godot

My tweens look like this for example.

card_texture.material.set("shader_parameter/mix_ratio", 1)
tween_damage.tween_property(card_texture.material, "shader_parameter/current_frame", 6, 0.1)