All game text is written in (poor) Portuguese, (or German, for those who understand Portuguese), and the central gameplay loop involves using your wands to determine their mechanics.

Puzzles do not lay bare their requirements and mechanics. Follows the 2-4-6 task of psychology as highlighted here

Game centres around communication without explicitly informing the player how/why/when to communicate. Abstract iconography on the UI renders syntactic association for the buttons difficult.

Edge case: Features a minigame where the player plays Double Fanucci against the jester. It is intentionally complicated as a parody of other card games, similar to Fizzbin from Star Trek. The only way for the player to win is not to actually determine the rules however, but to utilise a strategy outlined in the game's feelies.

The player is never explicitly told how to solve puzzles, and the hidden mechanic of the game is entirely absent from the core puzzle loop for the player to find themselves.

Everything is completely abstracted from the player, with all text being written in a fictional script not analogous or translatable to any human language. This includes score.

Suggested by unverified cam man

While the controls are explicitly tutorialised, the deeper mechanics are obscured for the player to determine themselves.

Suggested by Beach_Episode

Tutorialisation of controls but nearly everything else in the game is hidden from the player, especially its deeper mechanics, story, and gameplay.

Suggested by chandler

Many items and characters unlock requirements are completely hidden from the player. Most notably, The Lost, The Forgotten, and the Ascent have incredibly complicated means of being accessed.

Suggested by chandler

Suggested by chandler

Pre-1.12 Minecraft did not include the recipe book, leaving crafting results entirely hidden from the player. Accessing The Nether and The End are also not made explicitly clear, alongside mechanics like ore spawns, block interactions, and even redstone.

Suggested by chandler

Intentionally hides information from the player as for how to proceed. This is done out of malice, rather than for the sake of the player discovering these obtuse mechanics.

No text in-game, leaving the player to determine the criteria for each puzzle on their own based on the Clutter series' iconography.

Suggested by Drax

See: The Witness

Maybe an edge case? In attempting to replicate the feel of STG, Toaplan's falling block puzzler features mechanics which aren't mentioned on arcade flyers or the cabinet itself. Some of these you pick up on pretty easily like that you can move falling blocks in the middle of a chain, but there are also numerous hidden bonuses which are critical for high score runs.