What happened before:
"See you in 30 seconds," Stark smiled as he stared at Aphex, pure insanity in his gaze.
BOOM!
The beam of [Moonlit Obliteration] hit him directly.
-99,999,999!
There was no need to even show the number, Stark was instantly killed, every cell in his body evaporated from the sheer power of that thing.
"..."
And the most important thing to note was that when dying, Stark could indeed feel the pain you would usually go through if you actually died.
When he was cut in half by Judicator, when he was swallowed by the sculk of the Warden, or when he was crushed by the Guardian Ape.
He felt it all, yet still didn't abandon because of the pain.
He needed to keep going, no matter what.
Funny enough, Aphex wasn't the first opponent Stark fought that use the moon as his power: there was Akira from the second trial.
BOOM!
[You have been killed.]