Effects that care about the tapped/untapped state:
* Many effects specifically target untapped creatures or permanents:
* Examples: "Target untapped creature you control gains +1/+1 until end of turn." This effect would not work on a tapped creature.
* Some effects trigger when a creature becomes tapped:
* Example: "Whenever a creature you control becomes tapped, draw a card." This effect would trigger if a creature you control becomes tapped.
Effects that don't care about the tapped/untapped state:
* Many effects simply target creatures or permanents regardless of their state:
* Examples: "Destroy target artifact." This effect would work on a tapped artifact.
* Some effects target cards in hand, graveyard, or library, which are unaffected by being tapped:
* Examples: "Counter target spell." This effect would work even if the spell being countered is on a tapped creature.
Important Note: While a tapped creature can't attack or block, it still has all its other abilities and can be targeted by spells and abilities.
In Summary: Whether an effect works on a tapped card depends on the specific wording of that effect. Carefully read the effect's text to determine if it cares about the tapped/untapped state.