Beckoning Haunt

Action - XX

, destroy this: Return target aura with cost X from your graveyard to your hand.

Guardwell

When activating Beckoning Haunt, you must target an object with the aura subtype and a cost value of X, where X is any number greater than or equal to 0. When determining how many resources you must pay as part of activating this ability, you must pay a number of resources equal to essentially twice the cost value of the targeted card plus 1. When this activated ability resolves, you will return that targeted aura card in your graveyard to your hand.
An aura with a cost value of 0 can be targeted. If the aura has an X within its cost value, treat any X in that cost value as 0 (e.g. X3 would be just 3). You cannot target an aura that does not have a cost value.

Guardwell - When the combat chain closes, if this defended, put -1{d} counters on it equal to its {d}

Guardwell is an ability keyword.
If a card with Guardwell has 0 when Guardwell resolves, no counters are put on the card.
A card cannot have negative . If an effect would reduce a card to less than 0 it only reduces it to 0.
If the card with Guardwell has defended and has 0 when the combat chain closes, no counters are put on the card when the trigger resolves.
Guardwell’s effect resolves before effects that last for “the/this combat chain” end. E.g. Shred’s effect will still continue to apply to the defending card when Guardwell is resolving.