Matthwe's ares NG+ hardcore run somehow managed to skip enemy spawns in the first lightning spike room in stage 6 accidentally, which saved him a few seconds. How is that possible?

If we can figure out exactly what location the game checks to start spawning the enemies, then it might be possible to skip the spawns, in much the same way that red key skip works.

I found out how this works, i check other rooms in the game.

Looks like every other room beside this one and red key, spawns the enemies, every time.

Yup I just tested it and that seems right to me.

I tried testing some other rooms like this in the earlier levels (most of the midbosses, etc), but a lot of them have screen scrolling (probably triggered by a sort of 'wall') that forces you to stop in place, making it impossible to jump over the trigger. It might be possible that some of the levels from the original games have arena fights that can be skipped by avoiding their floor trigger. Of course, its possible that they also have 'wall' style triggers instead of floor triggers, but it might also be that they have really tight spacing.