Activate Viscera Seer by sacrificing Optimus Prime, Hero.
When Optimus Prime, Hero dies, its second ability triggers, returning it from your graveyard to the battlefield as Optimus Prime, Autobot Leader.
Activate Viscera Seer by sacrificing Optimus Prime, Autobot Leader.
When Optimus Prime, Autobot Leader dies, Mikaeus triggers, returning Optimus Prime from your graveyard to the battlefield as Optimus Prime, Hero with a +1/+1 counter on it.
Resolve both Viscera Seer abilities from steps 1 and 3, causing you to scry 1 twice.
Repeat.
This clever loop turns Optimus Prime, Hero into an endless sacrifice engine by taking advantage of the creature's dual-faced nature and its interaction with Mikaeus, the Unhallowed. When you sacrifice Optimus Prime to Viscera Seer, its death trigger returns it to the battlefield converted as Optimus Prime, Autobot Leader, bypassing any counters because it technically enters as a new object. When you sacrifice that back-side form, Mikaeus grants it undying, bringing it right back to the front face with a +1/+1 counter—which is then conveniently cleared the next time it dies and triggers its own transformation ability again. This seamless alternating cycle lets you sift through your entire deck with endless scries while generating boundless death and sacrifice triggers.