I must correct what I said: in the nightmare intro the glitch works fine but the game will crash after the cutscene. No problem in the real Lakeside. All my tests were made using the PAL version of the game on my fat PS2 (SCPH-50004). My previous comment was referring only to turning the coaster off both in the nightmare and in the real Lakeside, sorry if it sounded a bit misunderstandable.

Hello everyone, some of you already know me from a couple different Twitch chats. I sometimes run the PS2 PAL version of SH3, easy/easy, just for fun, but I still haven't submitted my PB cause I don't have any capture card yet.
Anyways, today I did a few tests regarding the third ampoule. I got to the end of the Chapel with yellow health, on purpose, and found out that a medkit is enough to beat the final boss.
I equipped a medkit before using the Aglaophatis and used it after taking three hits from "god".
I repeated the same test 5 times and always survived. That means you can use two ampoules when running from/to Jack's Inn cause you don't need one for the final boss.
IMO, the easiest medkit pickup is the one in the Oxydol cabinet, in Hilltop, and as you all know the one on the train is on the route too. Picking up one or two extra items (you will most likely pickup a health drink from the cabinet too) will not mess up your menuing too much, also cause that section of the inventory is only used twice in the game (that is, if you have to equip the medkit before the final boss). Btw, the Roller Coaster Key Skip works perfectly fine on the PS2 PAL version of the game as well, both in the nightmare and later on in the game.
Sorry for boring you to tears with such a looooong and tedious comment, take care everyone 🙂