Holding Cells

Creatures enter the battlefield with 1 Shackle counters on them
Creatures with shackle counters have, "At the beginning of you upkeep, sacrifice this creature unless you pay {1} for each shackle counter it has."
{3}{t}: Put a shackle counter on each creature
"The cells may be for holding. But for how long is just a matter of how long you live."