Risk of Rain Returns: Unlock Requirements for All Characters

Commando – Unlocked upon launching the game

Huntress – Unlocked upon launching the game

Enforcer – Kill the Magma Worm, Wandering Vagrant, and Colossus once (does not need to be done in one run)

Bandit – Finish the teleporter event on Stage 3

Pilot – Collect 15 different Monster Logs (these are sometimes found after killing a monster that you do not have a log for)

Loader – Obtain 30 unique items in one playthrough

Mechanic – Purchase 40 drones total (does not need to be done in one run)

Chef – Obtain the following items in one run : Meat Nugget, Bustling Fungus, Bitter Root, and Foreign Fruit

Acrid – This character must be found and freed during a run to unlock. (unsure) Sunken tombs map in the top right corner of the map?

Miner – (?) Stage 4 Magma Barracks, tunnel in the bottom-right corner of the map which will lead to a named Elder Lemurian “Direseeker”. Killing this will unlock the Miner, but this tunnel is NOT always open.

Artificer – Visit 10 unique stages (does not need to be done in one run)

Drifter – Recycle 6 drones in one playthrough

HAN-D – Can be found on the final level in the “Cargo 2” area of the map. Interact with what appears to be a grey door to unlock.

Sniper – Beat the game once

Mercenary – Beat the game five times

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Thanks to wes for his great guide, all credit to his effort. you can also read the original guide from Steam Community. enjoy the game.