QoT 'mulch Shambler' ability needs this change*added second idea*
1)
When 'mulch Shambler' used one of your shamblers will charge in at their current target and explode.
Edit:
If they dont have a target as in running with you they stop moving when activated for 3-4 sec and blow up on the spot they stoped at.
2)
Alternative thought that may be easier. You press the mulch ability , select a target and one of the shamblers charges it and explodes.