Juice In Games (Psychology of Fun)

UI tweening and easing

Hit Effects and number feedback spawner

UI bounciness

Shockwave effect that ripples through the screen. E.g EverClimb

Slicing through objects effect

Satisfying button press: E.g One more press, Can We Make This Button Fun To Press?

Water Effects with swimming, these include trails and splash in/out effects

Screenshake