The Hero Trial
https://f95zone.to/threads/the-hero-trial-full-moon-higure.23678/
Normal mode is tough enough, at least the first and also the second area (of 3.5).
You should start with that to get familiar with it, and maybe a second "normal" run trying to optimise.
And only then, the hard mode. Which is ... baffling.
the game has no story and hardly character, but the tough puzzle part is excellent.
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The same gameplay, but compared to "Hero Trial" more lenient in normal mode and hard mode is in
Dungeon of Luluu Farea,
https://f95zone.to/threads/the-dungeon-of-lulu-farea-kill-screw-marry-galaxy-wars.2612/
and it is by far the better game - has a story (well ...) and good characters, good dialogues, often very funny.
Hard mode is harder than normal mode, which already has every player running into dead ends and restarting all over, several times, but also hard mode is not as much fun, in an optimised normal mode run you can buy things at the very best possible timing and it gets a nice flow.
For an extra challenge, you can try to play normal mode with trying to have the most yellow keys at the (succesful) end of the game
(of course without buying any at the market, but also of course buying from dungeon fairies is fine).
See if you can beat me - will have to look up the exact number I ended up with (112? 124? sth. like that).
Or you can try to beat a highscore, for which hard mode is necessary and a significantly different playstyle.
(Score calculation gets explained in the game)
I strongly recommend
the old WolfRPG version, fantranslated to good English, has more content and looks better than the rpgmaker remakes.
It also has a sequel, but there the puzzle is significantly more lenient in normal mode (still some fun) and hard mode is more messy and annoying/ laborious than hard.
Characters and dialogues are still good in the sequel.