Is it possible to create a similar situation to Keen 1 in which Keen doesn't start with a pogo and must get some item (ideally the grappling hook, stupendous sandwich, or rocket pass) to regain his pogo ability?
Hmmmn, interesting. I imagine it would be more difficult than in Keen 1-3, since Keen has the pogo ability from the start, so you can't just turn it off. (As far as I know there is o variable tracking the pogo at all.) Stopping the pogo irreversibly is easy enough though.