I think I might have figured out the solution to the Taxing 18 challenge, as long as I don't run out of builders. I'll have to test my solution to see if it works...

Anyway, here's a few more challenges:

Lemmings:

Fun 20 - We are now at LEMCON ONE: Save 100%. using 8 builders, 1 basher, 2 diggers, a climber, and a floater.

Fun 22 - A BEAST of a level: Save 100% with no bridges.

Fun 23 - I've lost that lemming feeling: Save 100%. using all three exits.

Taxing 19 - Bomboozal: Save 92% (65/70) in one minute.

Mayhem 5 - Down, along, up, in that order: Save 95% (76/80).

Mayhem 15 - The fast food kitchen: Save 100% in less than 2 minutes.

Mayhem 29 - Save Me: Save 95% (76/80).

ONML

Crazy 20 - Ice Ice Lemming: Save 100%

Wild 13 - Onward and Upward: Save 96% (77/80).

Havoc 19 - Looks a bit nippy out there: Complete the level without using the bottom 2/3 of the level.