The name "Hider" describes a set of closely related roles. Each of them are active roles in which the user flavourfully "hides behind" the target of their night choice, typically making the user less vulnerable to actions used directly on them, but more vulnerable to their target and people attacking their target. However, the details vary by version.
The Normal version of the Hider is one of the simplest: the Hider, when they use their ability, cannot be killed by actions targeted at them; however, if their target dies as a result of an active killing action (e.g. a factional kill or Vigilante shot), the Hider will also die.
Some moderators treat kills performed on a Hider's target as being copied onto the Hider, rather than having the Hider's death trigger off the death of the hidee. This would change the result if, e.g., a Doctor was targeting the hidee directly (the variant Hider would die in that situation, whereas a Normal Hider would survive).
Some moderators cause hiding to apply to things other than kills. This commonly happens defensively; instead of being Bulletproof against direct actions while hiding, the Hider would be treated as a Commuter for direct actions. When treating actions as being copied (as in the previous variation), actions other than kills might also be copied; so the Doctor would now protect both targets, but a Cop would (perhaps unexpectedly) get two results. Note that this variant can lead to action resolution issues.
Use & Power
The Weak variant of Hider is a fairly powerful investigative role due to its ability to investigate and self-protect at the same time. It would be best to treat a Weak Hider as an inferior Cop that will have to play differently to deliver innocents and guilties.
A pure Normal Hider is, perhaps paradoxically, a substantially weaker role than the Weak variants. In the best case a Normal Hider is conditionally Bulletproof: by hiding behind players who are unlikely to be killed, such as the scummiest looking player, the Hider will effectively protect itself. This tactic may backfire if a Vigilante is in the game, so when balancing the game, you may need to allow both for the Hider hiding behind the Vigilante's target, and a Hider failing to hide Night 1 because they're waiting to see whether the setup contains a Vigilante or not.
It's important to be sure of the wording of Hider PM to ensure that they only die if their target is killed, as opposed to their target simply dying (such as a Suicidal Townie). Although, some mods may consider this to be a feature, not a bug!
A standard Hider should opt to protect the player they believe most strongly to be scum, effectively becoming bulletproof for the night. While a Hider may gambit to draw a night kill, unless the setup seems to reward this type of play, a Hider should simply try to be as town as possible. Managing to draw a kill as a Hider is a two-for-one deal: a kill on a Hider is not a kill that is likely to succeed on other members of the Town, and a kill on a Hider is not a kill on their target, further adding to its power.
A Weak Hider has two options:
1) Hide behind the least likely town kill, becoming unkillable for that night and confirming that person as town.
2) Hide behind the player most likely to be scum: and make no secret that if you end up dead, that is what likely happened during the night phase. This can effectively be a guilty on a player.
As with all Weak roles, it is best to leave a breadcrumb so that if you die, players can in retrospect work out who you must have hidden behind.
Sample Role PM
Welcome, [Player]! You are a Town Hider.
- Hide: Each night phase, you may target another player in the game to hide behind, rendering yourself immune to all nightkills that phase. However, if your target dies that phase, you also die.
- You win if all threats to the town are eliminated and at least one town-aligned player is alive.
Any Weak role offers information in the same way the original Hider did.
A Commuter may choose each night to commute out of town, becoming untargettable by any night action.
A Bulletproof player is immune to night kills.