General rule: If a card is in play, its text will be active and its ability will take effect.

Some cards can clear card effects, or prevent effects from happening.  If a card doesn’t work, it’s probably because another card stopped it!  <Looks at Cosmo>

Some cards will activate their abilities while they’re in your hand

For example: If Wolverine is in-hand and he is discarded or destroyed, his ability will activate.

Cards generally don’t have their ability active while they’re in your deck.

For example: Yondu can remove Wolverine/Colossus while they’re in-deck.

However, some cards specifically function while they’re in-deck, like M’Baku or Domino.