Anka, Drag Under (Yellow)

Action -

: Attack

Instant -

, discard a card with watery grave: The next time an opponent draws one or more cards this action phase, they discard a card.

Watery Grave

When Anka’s instant activated ability resolves, it generates a delayed triggered effect that triggers the next time the opponent draws one or more cards. That opponent will discard a card when that triggered effect resolves.
Anka’s effect does not trigger when cards are drawn during the end phase. If a player draws one or more cards from another effect (e.g. Ponder) or draws cards up to their intellect as an end of turn procedure, it does not trigger Anka’s effect.
If a player would draw one or more cards and trigger Anka’s effect, they finish drawing all of those cards, then when the triggered-layer resolves, they discard a card. There is priority between drawing the cards and resolving the triggered layer to discard a card.

Watery Grave - When this is put into your graveyard from the arena, turn it face-down.

Watery Grave is an ability keyword.
Watery Grave is a trigger that ONLY triggers if the card is put from the arena into the graveyard, excluding when it is a non-permanent defending card on the combat chain. It also does not trigger if it is put into the graveyard by other means (e.g. discarded from your hand, destroyed from the top of the deck, put into the graveyard from your deck).
When Watery Grave’s triggered effect resolves, you must turn that card with watery grave face-down in your graveyard.
Similar to face-down cards in the banish zone, you can look at face-down cards in your graveyard. Opponents cannot look at face-down cards in your graveyard.
Cards and effects that interact with cards in the graveyard cannot interact with face-down cards in the graveyard unless the effect specifies that it affects face-down cards. For example, if a card requires you to banish 3 random cards from your graveyard as an additional cost, face-down banished cards are unable to be banished from your graveyard this way to pay for the cost.

Cost2

Attack5

Life3