Tunic

A door with no keyhole plants a question players can't stop asking. Tunic puts a giant stone gateway at the top of a snowy mountain with no keyhole or handle, so players wonder both what is behind it and how it could ever open.

Dark Souls (Sen's Fortress), Super Metroid (the golden statue room), Hollow Knight (the black egg) and Spelunky (the Moai head) use the same device. Mark Brown: "A locked door is inherently mysterious because the player is left to wonder what's behind it - and to wonder how they'll ever open it."

Lock progress behind knowledge, not items, so solving feels earned. The mountain door has no key item. It opens only for a player who has pieced together clues from pages of the in-game manual scattered through the world.

Games that do this are called Metroidbrainias: the keys live in the player's head, so they can't be stumbled on and demand attention and even note-taking. The payoff shifts from "I found a key" to "aha, I figured it out!" Outer Wilds, Riven and Chants of Senaar work the same way.

Make the hunt fun and the reward behind it can be modest. Mark Brown loved the scavenger hunt for the mountain door's solution but cannot remember what was behind it.

The answer only matters when it gives away the answers to the game's other questions. Quote: "if the act of solving the mystery is really fun, then the answer doesn't particularly matter."

Andrew Shouldice deliberately leaves many loose ends for players to chase. Tunic has tombs too dark to explore and enemies too tough to fight, which designer Andrew Shouldice calls "paths into the darkness". He keeps many open because "curiosity and speculation is fun".

His favourite kind of game is one where "suddenly the entire path that you've traveled becomes littered with question marks." Mark Brown warns that each open door adds mental load, so the number of loose ends has to be managed.

Separate the required ending from the cryptic one so everyone can finish. Tunic has one ending for beating the final boss and another for players who solve its cryptic clues, so the hardest mysteries stay optional.

Few players will crack the trickiest puzzles, so the designer has to decide which mysteries are required. Fez (32 cubes to finish, with many secrets after) and Animal Well (built in three layers, the last needing community help) use the same layering.

Accessibility options let players skip hard bosses and still enjoy the secrets. Tunic's accessibility options let Mark Brown's wife tone down its Souls-like bosses so she could enjoy its secrets and riddles. Hollow Knight and Silksong offer no such option.

Challenge is subjective, and adjustments stop players missing exploration or lore because they can't beat a boss. Quote: "Difficulty adjustments let everyone find a place where they feel challenged."

Its Golden Path rewards following one puzzle thread at a time. Mark Brown cites following the Golden Path in Tunic, like chasing the quantum moon in Outer Wilds, as the single-thread puzzle chase that Blue Prince's random room draft interrupts.

In Blue Prince the needed rooms may not appear, so methodical players get knocked off their thread and end up re-rolling.

Tunic is held up as a puzzle game that trusts players to think. Mark Brown lists Tunic with Return of the Obra Dinn, Outer Wilds and Immortality as games to play for a real mental workout instead of a hand-held blockbuster like God of War Ragnarok.

Quote: "if you actually want to engage your brain, you're probably going to have to look elsewhere".