This run has it all: Merl's 2 year old death strategy, which I recently rediscovered to be 2.3 seconds faster! 'flawless' bosses including 5-hit 2nd boss and 5-hit final boss!
Improvements can be made: On the screen grabbing the 2nd orb. Jumping was suboptimal there going in and out of the cave. Tiny micro improvements, optimizing/perfecting every little thing. Yes, also the bosses are not really flawless.
According to my analysis, this is a very high 2:47. I had a 2:48 which was just 4 frames slower. If this is true, this run cannot be faster than 2:47.93. Maxing out everything, I think .6 or .7 seconds can realistically be saved. But I currently don't see a way to save a full second here. Who knows what the future will bring?
Credits to Merl_ for the death strat: https://www.speedrun.com/user/Merl_
Credits to JackAa for beating the previous WR, motivating me to grind again: https://www.speedrun.com/user/JackAa
Leaderboards for this game and run can be found here: https://www.speedrun.com/demon_castle?h=Seal_Demon