Oh come on, Ballos isn't that hard. Half the fight is spamming rockets into his eye.
It took me many tries to get used to his pattern. I saved rockets for the last incarnation of him. Used an editor to add a save point in the Corridor. I doubt I'll finish this game with a clear Sacred Grouds - Ballos run, but maybe will do another full run in future. It may be interesting to fight him with the machine gun (the ultimate jet pack :)).
Also, there's a health glitch that gets you Hp each time you enter and exit the map, most notably after the cave-in section.
Never saw it. I've just tried, but couldn't reproduce it.
My own experience with the game, by the way, would place the Undead Core as being one of the easier bosses, especially if you actually bother to use your missiles, but both of the fights before it are pretty annoying, if not particularily difficult.
The opposite happens if you use rockets against Doctor. He dies very fast, but Core adds some problems. For the Core I had to figure that Sue and Misery are killable and must be killed first, then another attempt was lost due to -20 (AFAIR) ray when the Core is close to death. As usual, after studying the bosses they aren't hard.
Sacred Grounds was a cakewalk after the first room, but going through it every time you lose to Ballos is indeed pretty annoying, if expected, and I honestly don't think Ballos himself is that difficult.
Strange, the first room was by far the easiest.
You've got a false belief BTW.
That might need spoilers...Anyway, that's why you need to save an HP pot and use it before the battle. :P Don't be tempted to use one during the Undead Core battle, and ignore the Undead Core's lackeys and just hit the eye. :)
Yeap. I forgot about it the first time when I got the bad (or neutral) ending. The second time I used it for Undead Core just to find later that I really need it for Ballos :P2
Lackeys drop so much stuff that they can be killed almost for free. Afterwards the Core is easily predictable.