Rules FAQ
- If you only have one card in hand when Umber Loyalist leaves play, the ability does not trigger because "If an ability requires the choosing of [targets], and there [are not enough valid targets], the ability cannot be initiated."
House Umber.
Reaction: After Umber Loyalist enters play, draw 2 cards.
Forced Interrupt: When Umber Loyalist leaves play, choose and discard 2 cards from your hand.
Link: Decklists
Rules FAQ