Text (HL+errata): 3/3. ; Whenever ~this~ attacks, if defending player controls no black nontoken permanents, it doesn't untap during your next untap step. [Oracle 2007/05/01]
It checks for black cards only at the time you declare attackers. If there are any, it won't trigger. [D'Angelo 1999/08/01]
Note - This card was of creature type "Bear" until Oracle 2007/09/01 when it became "Bear Spirit".