Snake
offeringOffering is a static ability that functions while the spell with offering is on the stack. “[Quality] offering” means “As an additional cost to cast this spell, you may sacrifice a [quality] permanent. If you chose to pay the additional cost, this spell’s total cost is reduced by the sacrificed permanent’s mana cost, and you may cast this spell any time you could cast an instant.”
You choose which permanent to sacrifice as you make choices for the spell (see rule 601.2b), and you sacrifice that permanent as you pay the total cost (see rule 601.2h).
Generic mana in the sacrificed permanent’s mana cost reduces generic mana in the spell’s total cost. Colored and colorless mana in the sacrificed permanent’s mana cost reduces mana of the same type in spell’s total cost, and any excess reduces that much generic mana in spell’s total cost. (See rule 118.7.) (CR 702.48) (You may
castTo cast a spell is to take it from the zone it’s in (usually the hand), put it on the stack, and pay its costs, so that it will eventually resolve and have its effect. A player may cast a spell if they have priority. See rule 601, “Casting Spells.”
To cast a card is to cast it as a spell. (CR 701.5) this spell any time you could
castTo cast a spell is to take it from the zone it’s in (usually the hand), put it on the stack, and pay its costs, so that it will eventually resolve and have its effect. A player may cast a spell if they have priority. See rule 601, “Casting Spells.”
To cast a card is to cast it as a spell. (CR 701.5) an instant by sacrificing a Snake and paying the difference in mana costs between this and the sacrificed Snake. Mana cost includes color.)
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UntapTo untap a permanent, rotate it back to the upright position from a sideways position. Only tapped permanents can be untapped. (CR 701.26) all Forests and all green creatures.
ActivateTo activate an activated ability is to put it onto the stack and pay its costs, so that it will eventually resolve and have its effect. Only an object’s controller (or its owner, if it doesn’t have a controller) can activate its activated ability unless the object specifically says otherwise. A player may activate an ability if they have priority. See rule 602, “Activating Activated Abilities.” (CR 701.2) only once each turn.