This is Mayhem level 2, "Lemmy down". You have 99 lemmings and must rescue all of them within 10 minutes.
Turn the lead lemming into a Digger a small ways from the entrance.
Make the lead lemming a Builder, building steps over the right wall.
A few lemmings will walk leftward because the steps weren't complete and they turned around when hitting the wall. Make the last left-walking lemming into a Digger, close to the left wall. The lemmings walking rightward below will pick up a Floater ability.
Make the Digger lemming a Floater.
That lemming should then walk into the red teleporter.
The lemming will be cloned. They will pick up a Floater ability.
Make one of them into a Builder before the large drop to the exit.
Make a left-walking lemming into a Blocker before it reaches the red teleporter, but after the spot where the lemmings are falling into the lower area.
The Builder should collect a Basher and Bomber ability.
Increase the entrance rate of the lemmings to 99.
Have a trapped lemming dig through the right wall.