Dinrova Horror

When Dinrova Horror enters, return target permanent to its owner's hand, then that player discards a card.

Pioneer Masters

"Welcome to the Dimir Public Offices. Not responsible for death or loss of property. Basement off-limits."
—Sign outside Dinrova Building

Jumpstart

GRN Guild Kit

When Dinrova Horror enters the battlefield, return target permanent to its owner's hand, then that player discards a card.

Battlebond

Modern Masters 2017

A token permanent returned to a player’s hand isn’t a card and can’t be discarded. It will cease to exist when state-based actions are performed after the ability finishes resolving.

If a player has no cards in their hand and Dinrova Horror returns a card to that player’s hand, the player must discard that card. They won’t have the opportunity to cast that card (or do anything else with it) before discarding it.

If the target permanent is an illegal target when Dinrova Horror’s ability tries to resolve, the ability won’t resolve and none of its effects will happen. No player will discard a card.