You can do this on your own.
Make AI Practice game, play as Tainted Coil against Most Gentle Drowning Doom on Feeding Ground.
Capture the geysir on the right and keep defending it until you can make a Pain Lifter (or an upgraded Pain Lifter).
Keep killing Ophelia as much as possible, so she can't upgrade. That way she will only spawn basic units. At some point she will spawn 3+ units (18 single units) of Gravediggers and keep them at the stage.
Place your Pain Lifter on the path between her stage and your geysir. Ophelia will eventually advance with her 3+ units of Gravediggers against your geysir. Double team (by pressing Y) and fire the Pain Lifter and make it explode a little above ground by pressing A.
Hopefully you will be able to take out all the Gravediggers in one blast. If not, just keep trying. The clue is to keep Ophelia from upgrading to more powerful units or veichles.
This worked for me at least.
(Same tactic can be used for Ringleader and Painkiller, using Ironheade against Drowning Doom, or Dollpocalypse using Drowning Doom against Drowning Doom)