FearFear is an evasion ability.
A creature with fear can’t be blocked except by artifact creatures and/or black creatures. (See rule 509, “Declare Blockers Step.”)
Multiple instances of fear on the same creature are redundant. (CR 702.36) (This creature can't be blocked except by artifact creatures and/or black creatures.)
When this creature enters, you may pay
. If you do, target creature gets +X/+0 until end of turn.
When this creature enters,
sacrificeTo sacrifice a permanent, its controller moves it from the battlefield directly to its owner’s graveyard. A player can’t sacrifice something that isn’t a permanent, or something that’s a permanent they don’t control. Sacrificing a permanent doesn’t destroy it, so regeneration or other effects that replace destruction can’t affect this action. (CR 701.21) it unless
was spent to
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) it.