Tiara of Suspense

Instant - Destroy this: Put a suspense counter on an aura of suspense you control. Activate this only if you've been cheered this turn.

Guardwell

Rulings

From the Super Slam release notes

When Tiara of Supsense’s activated ability resolves, you choose which aura of suspense to put an a suspense counter on at that time.

Keyword notes

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.