From Worms Knowledge Base
Contrary to what the name implies, this is a transport tool, not a weapon of war. When selected, your worm dons a crash helmet, sticks a steriotypically designed sling-shot in the ground and sits in the rubber pounch, his tail pushing against the stick. Like the Baseball Bat, it can be aimed anywhere from the horizontal up to a certain angle of about 45 degrees.
When activated, the rubber band is released and the worm is propelled into the air at the angle chosen. The effect is similar to the Baseball Bat, only your worm is not propelled quite as far as with the Bat, and does not take specific damage from it. Your worm takes fall damage, if any, but the crash helmet prevents the loss of the turn, allowing your worm to continue as normal after usage of the Catapult.
This weapon, if it can be so-called, is very similar to the Baseball Bat in its effects, only the worm who uses it is the one who gets propelled by it. Preventing damage and cancelling the loss of turn should be simple enough. Animation should be straight forward.
This would have its uses for navigating difficult terrain where other transport options weren't available or suitable. Crossing a large pit or climbing up to a high ledge would be among the top uses for this tool, but there is the risk of mis-judging the angle and the uncertainty of what happens to your worm when he lands.
This weapon isn't much different from the Low Gravity utility when you think about it, perhaps only a little more powerful. And the Low Gravity utility has so many more uses. Then again, the Low Gravity can only cover limited distances, and the Catapult doesn't last the entire turn, so it may be the more useful option when Low Gravity is inconvenient.