Drowning Doom team are availible only on Multiplayer.
I suggest go to Practice and easy difficulty or custom and play only your own team against no one.
Ophelia needs to double team with the entire unit available.
There are 10 Units to double team and are split into default and 3 stage upgrades.
Default: Gravedigger, Bride and Frightwig
Level 1: Ratgut, Lightning Rod and Organist
Level 2: Brood, Dirigible and Reaper
Level 3: Tree Back
When you team up with the entire team, you'll earn the trophy.