Slave Processing Facility

Facility (This artifact can hold abducted creatures.
If it is destroyed, return all abducted creatures to the battlefield under their owner's control.)
{t}: For each color among abducted creatures
kept in this facility, add one mana of that color.
{6}: Destroy this facility. This ability costs {1} less
for each abducted creature being held captive.
Any player may activate this ability.