Giant Trap Door Spider — ruling 1

If Giant Trap Door Spider leaves the battlefield before its ability resolves, the ability will still resolve as normal. The targeted creature will be exiled.

Giant Trap Door Spider — ruling 2

If the targeted creature leaves the battlefield (or otherwise becomes an illegal target) before the ability resolves, the ability won’t resolve. Giant Trap Door Spider will remain on the battlefield.

Giant Trap Door Spider : règles, fonctionnement et interactions (MTG)

Giant Trap Door Spider is one of those cards players keep asking about. Here is, in plain words, what its official text says, the rulings published by Wizards of the Coast, and the combos players actually run.

Official card text

, : Exile this creature and target creature without flying that's attacking you.

How it works : Giant Trap Door Spider

Original English text — Wizards of the Coast / Scryfall

#1October 4, 2004· Wizards of the Coast
If Giant Trap Door Spider leaves the battlefield before its ability resolves, the ability will still resolve as normal. The targeted creature will be exiled.
No other card is named in this ruling.
#2October 4, 2004· Wizards of the Coast
If the targeted creature leaves the battlefield (or otherwise becomes an illegal target) before the ability resolves, the ability won’t resolve. Giant Trap Door Spider will remain on the battlefield.
No other card is named in this ruling.