Carrier

Carrier is creature type originally unique to Urza's Legacy. It first existed as a vertical cycle of four black Phyrexian creatures which spread disease. Otherwise, they could have been just Horrors.

The Cycle

Each of these creatures can be sacrificed to give another creature -X/-X until end of turn, where X is its power and toughness.

• Phyrexian Denouncer (1/1)
• Phyrexian Debaser (2/2)
• Phyrexian Defiler (3/3)
• Phyrexian Plaguelord (4/4)

Note

• The white card Carrier Pigeons doesn't have the subtype Carrier.
• More surprisingly, the black Disease Carriers from the set preceding Urza's Legacy (Urza's Destiny), with a similar design, hasn't the Carrier-type either.
• The same can be remarked concerning Maggot Carrier from Planeshift.
• It would not be until Modern Horizons that another card with the subtype was seen, this being Plague Engineer.