Fear

Fear is a keyword ability found primarily on black creatures. It is an evasion ability that allows a creature to only be blocked by black or artifact creatures. The ability has existed since Alpha, where it was printed on a card called, appropriately, Fear. The rules text of that card was originally the rules text for the fear ability. The ability was first keyworded in the Onslaught set. All pre-Onslaught cards have been errataed to replace the older rules text with the fear keyword. The Fear keyword, lifelink, and the vigilance keyword are the only keywords with a card of the exact name. Flying comes close, with the card called Flight.

Wizards has stated that Fear will no longer be used on new cards, in favor of the new keyword Intimidate. Intimidate differs in that nonartifact creatures can block the creature if they share a color with the blocked creature. Thus, Intimidate can interact with color-changing effects, and a nonblack deck can be built to use it against black creatures.

From the ()

Rulings

Cards that change color words do not change the Fear ability. The reminder text on the card can change, but it's just reminder text and does not actually define the ability.