When Animate Dead enters, it trigger, returning Angel of Indemnity from your graveyard to the battlefield and attaching Animate Dead to it.
When Angel of Indemnity enters, it triggers, targeting Dance of the Dead.
Holding priority, activate Shilgengar by sacrificing Angel of Indemnity.
Resolve the Angel of Indemnity trigger, returning Dance of the Dead from your graveyard to the battlefield.
When Dance of the Dead enters, it trigger, returning Angel of Indemnity from your graveyard to the battlefield and attaching Dance of the Dead to it.
When Angel of Indemnity enters, it triggers, targeting Animate Dead.
Holding priority, activate Shilgengar by sacrificing Angel of Indemnity.
Resolve the Angel of Indemnity trigger, returning Animate Dead from your graveyard to the battlefield.
Repeat from step 2.
This ingenious resurrection loop uses Shilgengar, Sire of Famine as a grim sacrifice engine to fuel an infinite cycle between Angel of Indemnity, Animate Dead, and Dance of the Dead. Whenever an animation aura brings back the Angel of Indemnity, its entrance triggers the return of the *other* aura from your graveyard to the battlefield, constantly passing the baton back and forth. Before each resurrection trigger can resolve, Shilgengar, Sire of Famine happily accepts the sacrificed Angel to generate Blood tokens, turning the recursive loop into an endless harvest of death and artifact triggers.