Offering

Offering is a keyword ability that allows a player to sacrifice an appropriate permanent to play a card with Offering as an instant and at reduced mana cost. It was introduced in Betrayers of Kamigawa in the five card "Patron" cycle, and has not been reprinted since.

From the ()

Rulings

Sacrificing the creature for the offering is part of the announcement of the spell. No player has priority to respond to an offering until after the creature spell is on the stack.
You may sacrifice only one creature when using the offering ability. Multiple sacrifices aren't allowed.
Effects that don't allow a player to play creatures also stop a player from using the offering ability.
Using the offering ability changes the normal result when calculating total costs [409.1f].
With [Object] offering, you may sacrifice an [Object] with a converted mana cost of 0. You have to pay the full mana cost for the Patron, but this allows you to play it whenever you could play an instant.
Colorless mana in the sacrificed creature's mana cost can only reduce generic costs. Colored mana in the sacrificed creature's mana cost reduces colored then generic costs. For example, offering a Fox that costs would reduce Patron of the Kitsune () to . Offering a Fox that costs would reduce Patron of the Kitsune to .
The cost reduction is calculated after cost increases. A Patron of the Kitsune with a Sphere of Resistance in play would cost . Offering a Fox with a mana cost of would cover all of the Patron's cost to play.
Offering reduces the total cost of a spell. The converted mana cost of the spell remains the same.
The creatures with the offering ability are Patron of the Akki, Patron of the Kitsune, Patron of the Moon, Patron of the Nezumi, and Patron of the Orochi.