Terrain

Not to be confused with Terra, the world where the game takes place.

“	Make good use of special terrains and mechanisms on some maps.	”
	—Loading screen tip

In Arknights, there are a number of terrains – unique tiles that bring advantages and disadvantages to friendlies and enemies when used correctly.

Terrain	Information
Protection Objective	The objective where enemies will try to enter. Should an enemy enters a Protection Objective, the player will lose Life Points depending on the enemy in question.
Incursion Point	Enemies will usually spawn into the map from an Incursion Point. Some operations feature Aerial Incursion Points from which flying units spawn.
Fence	Melee units can be deployed on a Fence, which is impassable for enemies.
Hole	If a ground enemy (and only ground enemies) is somehow forced towards a Hole (which is done by shifting them), they will be instantly defeated.
Bush	The friendly unit (and only friendly units) on a Bush becomes invisible even when blocking enemies.
Medical Rune	The friendly unit (and only friendly units) on a Medical Rune will have their HP restored every second, which stacks additively with HP regeneration bestowed by skills and talents.
Defense Rune	The friendly unit (and only friendly units) on a Defense Rune will have their DEF increased.
Anti-Air Rune	The friendly unit on an Anti-Air Rune will have their ASPD reduced but deals more damage against aerial units.
Specialist Tactical Point	The friendly unit on a Specialist Tactical Point will have their shift force increased, which is only relevant for those capable of shifting enemies.
Active Originium	The unit on an Active Originium will receive an temporary effect that increases their ATK and ASPD but causes them to lose HP (actually taking True damage) over time.
Heat Pump Passage	The Heat Pump Passage periodically erupts, dealing True damage to units on it (the eruption interval and the damage dealt varies with the operation).
Corrosive Ground	The friendly unit (and only friendly units) on a Corrosive Ground will have their DEF halved.
Tunnel	Enemy units who moved into a Tunnel Entrance will be moved into the Tunnel Exit of the same color after a delay that varies depending on the operation they are featured in.
Lava Crack	Introduced in Heart of Surging Flame, the Lava Crack periodically sprays magma to the surrounding tiles, which deals True damage to friendly units (and only friendly units) including Roadblocks, which will be instantly destroyed.
Stump	Introduced in The Great Chief Returns, the Stump is treated as a ranged tile, allowing friendly ranged units to be deployed on it, and appears in place of a Giant Mushrooms destroyed by Rhodes Island Temporary Employees. The Stump can be destroyed by Tiacauh Shredders and The Big Ugly Thing, permanently making it undeployable and instantly KOing friendly units deployed on the Stump.
Mark of Hui and Ming	Introduced in Who is Real, the friendly unit deployed on a Mark of Hui and Ming will have their Hui and Ming attribute set to either Hui or Ming depending on the Mark's color (black for Hui, white for Ming).
Mark of Dusk and Dawn	Introduced in Who is Real, the enemy unit passing through Mark of Dusk and Dawn will have their Hui and Ming attribute switched.
Gas Spray	Only appearing in Multivariate Cooperation: Defence Protocols, the friendly unit deployed on a Gas Spray will lose HP (actually taking True damage) over time.
Deep Water Zone	Introduced in Dossoles Holiday, friendly units cannot be deployed on a Deep Water Zone unless with a Custom Floating Platform, and enemies will have their ASPD and speed reduced, and lose HP (actually taking True damage) over time when they are forced to swim through it, or drown to their defeat in certain operations.
Icy Surface	Introduced in Break the Ice, friendly and enemy units on an Icy Surface will always be inflicted with Cold and Frozen enemies will also receive increased shift force. There are also Ice Streams which changes the direction enemies on it are to be shifted instead of increasing the shift force they received.
Nethersea Brand	Introduced in Stultifera Navis, the Nethersea Brand will periodically spread to nearby unoccupied melee tiles, which periodically deals Arts damage and inflicts Nervous Impairment to friendlies on them; Sea Monster enemies on the Nethersea Brand have the Nervous Impairment they inflict increased. Certain Little Handy components can mitigate the Nethersea Brand's effects.
Mire	Introduced in What the Firelight Casts, units on a Mire have their ASPD gradually reduced; enemies have their speed gradually reduced as well.
Reeds	Introduced in What the Firelight Casts, camouflages the friendly unit on Reeds. Certain enemies can ignite Reeds, causing the friendly on it to lose the camouflage and receive Arts damage/Burn Damage over time, which can spread to nearby unignited Reeds and can be extinguished by deploying a friendly over a burning one.
Yumen Catastrophe Defense	Introduced in Where Vernal Winds Will Never Blow, basically a ranged tile that is also treated as a melee tile which can be passed by enemies should they head through Ladders. Units over a Yumen Catastrophe Defense deals/takes more/less damage to non-flying targets outside them.
Clear Water	Featured in Reclamation Algorithm, friendly units other than Crabbie Pumpies, which generates Fresh Water over time, cannot be deployed on a Clear Water unless with a Custom Floating Platform while enemies can freely swim through it.
Makeshift Walkway	Featured in Hortus de Escapismo, allows friendly unit deployment and enemy movement on top of it, but will break and turn into a deadly pitfall after being struck enough times by rocks from Crumbling Masonry unless if a friendly is deployed over the Walkway. Broken Walkways can be repaired by using Spare Timber.
Transit Point	Featured in Trials for Navigator, enemies that enter will be removed from the current wave and included in a next wave, spawning from another Transit Point in that wave's zone.
Lava Fissure	Featured in Design of Strife, periodically erupts to deal Arts damage to nearby friendly units over time. If a friendly unit is deployed on top of the Fissure, it will cause magma to flow ahead whenever it erupts, which can damage enemies and amplifies the Arts damage they took for a period of time.