@androidarts Cool as arm cannons are, how do you climb a ladder without both hands? (page actually pictures Samus as example):
https://tvtropes.org/pmwiki/pmwiki.php/Main/ArmCannon

@60sRefugee Since Samus has a grapple hook thing in Super Metroid I suppose she could use a smaller version of that, like a little captain hook tractor field projection at the muzzle.

Metroid 1 has no ladders or edge climb movement (often to Samus' detriment as she gets stuck all the time).

IIRC, Mega Man 1 (on the NES) has normal hands that morph into the buster cannon only when he shoots.

Another idea is a Dalek plunger that appears out of the barrel.