My thoughts on all the edge cases and interactions. I'll start with the ones I think are most clear-cut, and move on to ones where I haven't made up my mind....
Jumper -> Bomber/Stoner: Definitely instant. At the moment, bombers are instant if they are in mid-air (fallers, floaters/gliders, shimmiers), so there is a straightforward consistency argument for making jumpers bomb instantly.
Non-climber Jumper hitting a wall: Fall facing the other way. As namida said, this is a normal way for a lemming to interact with a wall in front of them, and there's a lot of potential for situations where it's hard to turn a lemming around and the architect doesn't want to give a builder or walker because of backroutes, or situations where the player just has to decide which skill is least needed elsewhere. (Indeed, I remember using this to solve a Lemmings 2 level on one of the very few times I've played that game
)
Swimmer -> Jumper: Forbid assignment. Jumping out of the water is unrealistic, but making the skill do something completely different, as WillLem suggested, would be a weird edge case where a skill has two unrelated effects in different circumstances. These are hard for new players to discover and internalise, and should be avoided where possible. [EDIT: Namida posted with basically the same response while I was typing this.]
Jumper -> Walker: Forbid assignment.
Jumper -> Glider: Start gliding from the top of the jump. The only reason a glider normally has to go through the falling animation before starting to glide is that it takes time to pull the glider out; the start of a jump would also give the lemming time to do this. This would make the jumper/glider combination more powerful, and there is a lot of potential in making the combination of two skills able to access places neither skill can alone. (This is not like the above two cases -- in this case each skill
is doing what it normally does, we are just considering how they combine.)
To respond to Strato, this is
not inconsistent because
there is currently no other skill that jumps. Sure, we can look at the behaviour of a lemming walking off an edge to make comparisons -- such as my point above that a mid-air jumper should explode instantly -- but there are going to be differences as well as similarities. Jumping is jumping; falling is falling.
Regardless of what decision is made here, I would urge that if the lemming is already a glider, then the jumper skill shadow should show the full jump + glide trajectory.
Jumper -> Climber: Could go either way on this one. It works in Lix and has a lot of puzzle potential and I generally enjoy it. But there could also be a lot of puzzle potential in forbidding it, so that the player has to do more work to get into a position to climb. Forbidding it would provide a way for a climber lemming to turn, which is often hard; the flip side is that
allowing jumper -> climber would mean the player has to work to find a way for the climber to turn.
Climber -> Jumper (wall jump): This is intriguing because Lix never had this, so it would be distinctly new to Lemmings-like games (although familiar from many platformers, of course). However, if it ends up forbidden, you can still do a climb-bomber to make terrain for a later climber to jump from -- and having to weigh in the cost of the extra skill usage and lost lemming has puzzle potential in itself. I would strongly urge that we consider this one purely on the basis of whether we prefer allowing or forbidding it as a puzzle element and
not for "consistency"; no other skill jumps; there is no reason at the moment why a new player would expect this to go one way or the other.