climb from celeste. it'd help a lot with platforming, especially pre-booster 0.8/2.0. they could also change the last cave to have certain parts requiring some climbing. plus, it'd be able to let you grapple onto ledges with the tow rope!
i'd go with the bubbler. the fact you can hold that many shots without them actually firing, and yet still have them do contact damage at level 3 is kinda op. level 2 is good, and level 1 has to be the worst.