I love this thread.
(1) Shop Items (I never paid much attention to the shop)
(2) The glitch itself
I found a glitch in PlayStation R-Type 1 that I have been able to recreate 2-3 times, but I haven't found documented online (at least, when I looked years and years ago).
Why bring that up?
Because it was so frustrating when other folks couldn't recreate the glitch, even though I had isolated it to specific conditions (to the best of my understanding, anyway).
I don't have this game, sadly, but when I have "free time" and get my TED working, I'll investigate.
I played yesterday just for the glitch about11-12 times. I was using Bulkan instead of 3-way, speed up, 1 extra heart and the elixir. Played 8 times with the above setup but the glitch didn't trigger. I chose 2-3 times the 3-way (as when I discovered the glitch), speed up, 1 extra heart container, 1 elixir. Still nothing. I then quited.
Today I played once with 1 credit to the fith Boss. No glitch.
Maybe being newbie in the game I chose fancy things from the shop that I don't remember. Sure thing for the glitch is the 3-way shot along with some unspecific items though...
I've only played the PC Engine version, and can't read Japanese, but I think this is what the shop items do:
Speed: ordered from slowest to fastest. You start in the middle. Speeding up is always the first thing I do.
Fruit: one extra heart.
Elixir: automatically refills your hearts when you get down to zero.
Heart: use this to refill one heart. You use items by hitting II twice in a row. Items are used in the order that they are displayed, left to right: you can't choose which is used first.
Circle: use this item to launch a bomb that hits all enemies on screen.
X: I'm the fuzziest on this item. I think it makes your shot more powerful for a short period of time.
Incidentally, I have the Super PC Engine Fan edition, and haven't encountered this glitch.
Thanks for your help, in the meanwhile I descovered most of the items. I think X is canceling incoming bullets.
Can you choose what help item to trigger each time or you trigger those with the turn you bought them?