With permission from runner Hodgey:

Notes for this level:

Originally I thought I'd have to produce a lava trap to prevent the heroes overrunning me, but killing them with their own boulder traps works too and is much quicker (~9 minutes down to ~4).

1. Dig to the skeleton to the east.
2. Dig to the heroes to the south and set off the nearby boulder traps to kill them.
3. Run the skeleton straight to the yellow keeper's dungeon heart.