Just another idea I thought of. This is an 'instant' skill in the same category as Walker, Cloner and Jumper.
When assigned, the Lemming accelerates straight upwards with a flame jet coming from their feet (or a jetpack). They continue until they hit their head on an obstruction or die by hitting a trap or the deadly ceiling.
Some thoughts on the mechanics and their uses:
* If the lemming is assigned a Shimmier just before they hit their head, they will latch on and attempt to shimmy across the ceiling.
* The lemming cannot be interrupted while rocketing skywards (even with a Walker), although they can be sacrificed in their current position with a Bomber or Stoner.
* A Rocketer will explode instantly when given a Bomber or when the countdown reaches 0 with the nuke.
* Cloning a Rocketer will create a 2nd Rocketer facing the other direction.
* Gliders and Floaters can be assigned the skill, and will fly straight up from their current position. After hitting their head, they will resume gliding or floating, whichever is applicable.
* Drowners can be assigned the skill and will save them from death (assuming they don't hit their head and fall straight back in the drink).
* Swimmers can be assigned the skill.
* Fallers can be assigned the skill.
* Jumpers can be assigned the skill.
* Blockers cannot be assigned the skill.
* Climbers cannot be assigned the skill.
* Lemmings performing constructive (e.g. Builder) or destructive tasks (e.g. Basher) can be assigned the skill and will stop their current task to become a Rocketer.
By itself, the skill can be used to delay a lemming but otherwise doesn't do much else. The skill's main use would be its synergy with other tasks, like reaching very high ceilings with a Shimmier, a degree of flight control with a Glider, or attempting to land on a Builder or Platformer's bridge above them while it is being built. As one example, if you need to traverse a stretch of water with a relatively low ceiling and don't have a Swimmer available, it can be traversed with a Glider and one or two Rocketers.
If the dead vertical direction is too restrictive, then it could be slightly changed to be a very sharp angle instead, so there is a small element of horizontal motion so they can land on high ledges (e.g. 4 pixels up for every 1 pixel across). Hitting a wall would act the same way as hitting the roof (not sure if the should instantly start climbing if they're a Climber).