Attunement

 is an active ability, which means it will only activate once the creature has a full bloodlust counter.  For a list of all Cards with this ability, click here! 

Variations
can appear as certain activation as a Vampiric Power, or with a chance to activate. It will always activate at the end of your turn.

Strategy
Some Vampire Lords Dark Gifts are powerful enough that you want to use them several times. Just make sure the creature with this ability lives long enough to activate it at least once.