Very cool animations, very detailed! I have some complaints regarding the controls and lvl design tho... Overall I liked the grapple mechanic, it has a lot of potential! But the hit box and level design made the aiming too precise in some segments. I think maybe if the grapple was faster, and the hitbox a little more forgiving, or maybe not even that, maybe making the levels in a way that the player has more response time to aim. Vertically, the grapple mommentum seems to have a relation to the distance you grapple the mailbox, where horizontally that doesn't seem to apply, which threw me off a bit (minor detail).
Overall I liked it a lot tho! Great vibes from it, would love to see a more detailed overworld, with different sprites for different levels exploring different alien bioms!