"The rules are clear. If you want to leave, you need only convince another to take your place."

Hell's Caretaker

{T}, Sacrifice a creature: Return target creature card from your graveyard to the battlefield. Activate only during your upkeep.

The List

Masters 25

{T}, Sacrifice a creature: Return target creature card from your graveyard to the battlefield. Activate this ability only during your upkeep.

Ninth Edition

{T}, Sacrifice a creature: Return target creature card from your graveyard to play. Play this ability only during your upkeep.

Chronicles Foreign Black Border

Hell's Caretaker can be the creature sacrificed to activate its ability, but it can't be the target of its own ability.

The upkeep step is before the draw step, after the untap step. Because the turn has already begun, creatures put onto the battlefield during your upkeep won't be able to attack or pay a {T} cost this turn.