×Briar will not expand to a new tile if doing so would violate a force arrow, but briar can grow over force arrows in the proper direction. This only applies when new briar growth is being generated next to the arrow though, so if briar has somehow grown on both sides of a force arrow a single root will be able to grow briar on the other side of the arrow in either direction. Orthosquares have no effect on briar growth whatsoever.

×Briar will grow overtop of checkpoints, but won’t destroy them, so checkpoints can still be used if the briar is cleared off of them again.

×Obstacles block briar growth.

×Briar holds down pressure plates that it has grown over.

×Briar will grow through both of these elements. Bombs are eaten without detonating, while kegs are detonated if briar grows onto their tiles.

×Briar will not grow through fluff; see also “Diagonal Growth” above. Briar will grow through tarstuff, possibly releasing tarstuff babies in the process if the remaining tarstuff is unstable.

×Briar will grow onto puffs, but doing this kills both the puff in that tile and the briar that grew there. Briar roots that grow over puffs will not then mature a segment of briar growth as they normally would. Other briar roots connected to that briar will still mature briar growth as normal.

×Unique among monsters, serpent-type enemies and gentryii are all immune to briar growth. Briar can expand diagonally through a gentryii chain.

×Invulnerable NPCs are not invulnerable to briar. Briar will still kill them if it grows over them.

×These are both destroyed by briar growth. In the case of seeding beacons, destroying the beacon effectively deactivates it. In the case of conquer tokens, destroying the token removes the ability for the player to use it, but doesn’t remove the requirement that it must be used to solve the room. Thus if a player hasn’t hit a conquer token by the time the last token is overgrown with briar, the room will be unsolvable.

×These are destroyed if briar grows over them, but this has no effect on the room. The room itself remembers that such a token is in effect regardless of whether or not the token currently exists. Even citizens generated after the token has been destroyed will still behave as though the token exists.

×If a temporal recording is in progress when the temporal split point being used is overgrown by briar, the recording in progress will be cancelled and Beethro will continue from his current position. This is the same as if Beethro were to drink a potion while a recording is in progress.

×Briar will grow over it and destroy it without any other effects. This includes all potions, horns, monsters, monster remains, tokens, etc.

×Bomb, Powder Keg, and Fegundo explosions will all destroy briar. Note that briar growing over a keg will cause the keg to immediately detonate, while bombs and fegundos do not detonate when overgrown. Along with puffs, briar growth is unusual for its ability to kill a flying fegundo outright.

×Closing any kind of door on a briar will remove it. Building a closed door or a wall (with builders or scripting) on top of briar will not remove it, resulting in briar being placed overtop of tiles it shouldn’t be able to be placed on.

×Briar on a bridge that collapses or a platform that is moved out from under it will be removed. This only removes the briar if it would be over a pit tile. Briar that is on a bridge or platform that becomes a water tile will not be removed.

×A “build pit” marker or a “remove item” marker will remove briar when acted upon.

×The pickaxe weapon will destroy briar when attacking (but not when pushing) a briar tile. Briar cannot be pushed.

×Active firetraps will destroy briar on them at the end of each turn, however this doesn’t prevent briar from growing onto them. If enough briar roots are connected together, this allows them to force growth through active firetraps.

×Puffs will not target briar, but they will attempt to move through it. Doing so results in the destruction of both the briar and the puff, and will form ice if this happens over water.

×If briar has grown over a fluff vent, puffs will still spawn every 30 turns destroying the briar (and the puff) as normal. If fluff has formed over a fluff vent, the fluff will expand normally, removing all briar in the way of the expansion while keeping fluff at the new locations where fluff would be stable. Where fluff would be unstable, a puff is spawned, and then the briar and puff are both removed. If the fluff is expanding into briar over water, ice will NOT be formed. Ice is only formed by puffs, not by fluff.

×Left-clicking on a briar root will reveal how many turns are left before the briar expands again. If multiple briar roots are connected, you will get a display of multiple numbers in the form X/Y = Z. In this case, X = the number of briar growth tiles connected to the root, Y = the number of roots that are connected together, and Z = the number of turns before the next round of briar expansion. For example 41/3=13 means that there are currently 41 tiles of briar growth, 3 roots, and that in 13 turns the briar will be ready to expand. Once it reads 2/3=0, that means that the first two roots will deal with the remaining briar growth, and the briar will expand on the next turn.

More generally, once Z = 0 the briar will expand after your next action. Z will be 0 once there are fewer briar growths remaining than there are briar roots. For a single briar root, this means that there must be no briar growths left, so the only number displayed is both the number of remaining briar growths and the number of turns before expansion.

×Left-clicking on withered briar or briar growth will highlight all remaining briar growths that are connected to the briar you clicked on.

×Normally using Ctrl-numpad5 (or whatever you have ‘wait’ set to in your settings) will skip turns until the end of the current cycle. This is useful for skipping ahead to roach queen spawns and tarstuff growth. When there is briar in the room, the turn you skip to won’t necessarily be a multiple of 30. The skipping will also stop on any turn immediately after briar expands.

×Briar cannot expand across a diagonal pit, but it can be connected across it. Whether or not it is connected depends on the history of the briar activity in the room. Consider a 2x2 square with the following elements: NW: briar root, NE: closed yellow door, SW: pit, SE: floor. Because of the pit, the root cannot expand to the floor tile. Now suppose that there was withered briar on the SE floor. Without waiting and observing what happens, we can’t know if that briar is connected to the root. The reason for this is that briar can be connected diagonally, and the pit doesn’t prevent the connection, only the initial expansion.

In this example, if the room started with the configuration given above (briar root, closed yellow door, pit, withered briar) the withered briar and the root would not be connected, and the briar would not expand past the door to the SE. If Beethro then toggled the door open, allowing the root to grow and connect to the withered briar, they would now be connected. Later closing the door would remove the orthogonal connection, but keep the diagonal connection, meaning that the briar would continue to expand SE past the door even though the root itself appears to be cut off from the growing briar.

×Place two contained briar roots where the only direction they can expand is through a single active firetrap. During expansion the first root will create briar growth on the firetrap and then convert the growth to withered briar. The second root will then (on the first turn) expand beyond the firetrap and mature one tile of growth to withered briar, or (on all subsequent turns) connect to the pre-established withered briar, generate briar growth adjacent to all exposed withered briar, and then mature one tile of briar growth to withered briar.

This creates briar that will grow much more steadily and gradually, with a much rounder and more organic shape than the usual square patterns. Predicting where the briar will grow is easily done provided you know the rule for briar root ordering (to determine which root is the second one) and briar growth selection (for where that root will mature briar on its next turn).

A side-effect of this set-up is that the briar becomes practically pickaxe-proof, since all removed briar growth will be regenerated every turn, and the more important withered briar will constantly be shielded by this growth.