Creature — Merfolk Wizard 1/1, 1{U/B} (2)
Uncommon
Fear (This creature can't be blocked except by artifact creatures and/or black creatures.)
{2}{U}{B}: Each unblocked creature becomes 4/1 until end of turn.
The murk of the Wanderbrine concealed unseemly rituals designed to bring out the worst in merrowkind.
Illus. Larry MacDougall

5/1/2008: An "unblocked creature" is a creature that attacked and wasn't blocked. Creatures aren't "blocked" or "unblocked" until the declare blockers step, so activating this ability before then (or after combat ends) will have no effect.
5/1/2008: Creatures stop being unblocked as the combat phase ends. However, they'll stay 4/1 until turn ends.
5/1/2008: Inkfathom Witch doesn't cause creatures to lose their abilities.
5/1/2008: If Inkfathom Witch is attacking and unblocked, it can make itself 4/1.
10/1/2009: The effect from the ability overwrites other effects that set power and/or toughness if and only if those effects existed before the ability resolved. It will not overwrite effects that modify power or toughness (whether from a static ability, counters, or a resolved spell or ability), nor will it overwrite effects that set power and toughness which come into existence after the ability resolves. Effects that switch the creature's power and toughness are always applied after any other power or toughness changing effects, including this one, regardless of the order in which they are created.
Legal in Vintage (Type 1)
Legal in Legacy (Type 1.5)
Legal in Classic (MTGO)
Legal in Commander
Legal in Modern