I don't blame you BY, I actually almost always died at that section as well. I would've tried to do something like Obey the game if I had more experience with LL. I also planned to include some power-ups, but they proved to be too ambitious for the amount of time I had left. I haven't thought of adding more rooms however. I was trying to add section only hazards, that would've possibly worked in multiple room arena.
As for the triggerwork, it was basically my RPG Maker days that helped me with actually making this read-able. In short, the first few events are counters (either point counters or time counters) and all the rest were triggers that would activate once that counter reached that number. The stuff at the bottom of the arena was to make sure the AI doesn't get stuck, it just checked where you were and if that number doesn't match the area you were in, the enemies would teleport there. I was also debating adding a secondary weapon (the magic staff) to push enemies away possibly, but ultimately dropped it.
As for lag, I usually start lagging at the cannons (so 70, not much longer

). I wanted to also make the colour of the tiles different in the areas with inverse gravity, but that made massive lag spikes, so I dropped it.