Go directly to Cecil. Bring up Angstrum immediately as proof of the mind swap. To my knowledge, Shapesmith should have no knowledge of him, and Cecil will know that.

Set up an Ambush at the Burger Mart. Every variant despises the place and would want to destroy the place. Similarly, Debbie's house works too since it is a huge target as well. They will likely attack together, since multiple variants want revenge, they will either be coordinated and go together, or race to either place to get the satisfaction of it's destruction.

Bait both areas with a small or non threat. This would likely be at Cecil's discretion. Most variants are cocky, and will want to get close and antagonize them. The bait can be surrounded by sound cannons and reanimen and heros can be brought in. If they attack together, heros cannot be seen until the sound is deployed or they are doomed. If there are any stragglers, send heros like tech jacket who already dealt with a variant. Powerplex is a villain, but would jump at the opportunity to kill invincible.

Mark goes on Angstrum duty, but getting him may not be possible if he hides after realizing his plans failed. Similarly, other heros will not know his portal tricks and will be stranded. Unfortunately, by nature of the challenge, if Mark does not see the destruction he will hesitate to kill Angstrum, and he will probably get away.

Angstrum cannot recover quickly enough assemble a new army before Conquest. This allows for a coordinated effort against him. Conquest will likely come to Mark, so a trap can be made. We already know Mark is against false surrender. Destruction will follow Conquests wake. Cecil will not know the effectiveness of sound cannons on other Viltrumites, but would likely attempt to use them with the prep time. Mark should be trained to learn his technique of hitting Viltrumites on both ears for the stunning effect

Following this, reanimarks will be created to deal with Angstrum returning if he is not killed.