I'm getting very close to releasing my "Pulp Action Game Challenge" called Castle Helios.
This game represents a prequel to one of my other game's--Wizard's Apprentice. At least story or lore wise.
It looks kind of like a metroidvania, but I'd describe it more as a puzzle and exploration game as you search Castle Helios for the keys to escape. (Pardon the typos in the screencaps.)
The moral of the story is, don't knock Pulp! I think most would agree there have been some great things to come out of it (in particular I think Eyeland and Life's Too Short are two of my favorites that are already available).
I had an odd thing happen, I was having trouble with the "firebot". nothing seemed to register - shot many fireballs at him - at his chest, at his head by floating right in front of his face - nothing seemed to work - then i got up under his arm and used the feather to leap up. his arm disappeared and he stopped firing. (forgot to screengrab this) i just stood there. i walked back and forth, then i shot fireballs at him and one by one they took out all his life. he had no fight left in him! he was frozen. when his hearts were gone, the rest of him disappeared and the key popped up but there was no sound, no dialog. so i walked back out the righthand door. and when i came back in, his arm was back, firing away, but he was still gone and the key was still there.
i ducked under the fireblasts, grabbed the key and continued on the adventure!
a little while later, somewhat lost in a good way, i came back into this room from behind the bot - he was BACK, firing away, but from this side there was no way to fight him (even with the ice block) - i couldn't even let him kill me to go back to my last save point. i was stuck.
i had to close out the game and come back to get to my last save. i'm worried that i'll have to go back through that door at some point and i won't be able to finish the game
You're not the first person to try to "get past" him. I was sure I prevented that from happening, but looks like I might have to put some more "artificial blockage" in place to prevent it trying to skip him (intentionally and unintentionally).
Based on your screenshots, and assuming you have collected the fire key, you should not have any need to go back through that area. If you close and re-open the game, continue your save and return to that room, and you have the key, he should be de-spawned though. Let me know if that is not the case.
Also, the hint to killing him was just after he shoots you have a window of time to shoot his chest twice.