The game will never explain this, but you can actually fix a Mortal Wound (red skull icon on the left side of the health bar) and get your Marine back to a Healthy state, thus avoiding an instant kill when your health reaches zero, allowing you to go down again and be revived again.

To do this, you need to use a Medical Stimm (healing consumable pickup) when your health is high enough so that the healing provided from the consumable, will go past the maximum length of your health bar (overhealing). The game will then display the message "Mortal Wound Healed" on screen. This can be done unlimited times as long as you have Medical Stims and enough leftover health while in Mortal Wound state.

Since Stims have different effectiveness based on difficulty (higher difficulty = lower effectiveness), the rule of thumb to understand if you can do this successfully, is to do so when you have around 70% of the health bar filled with True Health (red health).

Update: as of update 3.0 of 26 Sep 2024, Stimms now also restore Contested Health (white) into True Health.


There is a limit on how many times an enemy can be staggered (interrupted / made flinch) by heavy melee attacks (Kick / Bash etc.) or heavier weapon shots (Charged plasma pistol, Melta etc.).

Generally, I found this limit to be 3 consecutive staggers in a short time for most regular enemies. That means if you're facing for example a Tyranid Warrior, and you Kick / Shoulder Bash them up to three times in a row, they will be staggered each time consecutively, but the fourth time they will be immune to this effect and continue whatever attack animation they intend to do, which you will then have to forcibly dodge or parry.

Remember this to avoid being hit by an attack that you think would be canceled by stagger, only to find out it will not, as the limit of stagger has been reached. After like 5-10 seconds or so this limit will reset and you can stagger again the same enemy up to 3 times with heavy combo attacks or ranged.

The above does not apply to Bosses with a big health bar and Extremis level enemies (such as Zoanthrope, Lictor, Terminator etc.).


In Operations, there are always three classes of parrying for all melee weapons. They work differently and allow you to do different things: Blocking and Parrying, or both. In Operations, ALL melee weapons always have a variant of each Parry class in each tier starting from Green.

A Parry happens when you time your defensive animation correctly, and will stagger the enemy, or instantly kill them if they are a Normal class enemy (small tyranids, small chaos demons). Parries can be performed on ANY attack not just the blue-highlighted ones, but can NOT be performed on Orange-glow attacks which are unparriable. A parry always staggers the enemy regardless of the Stagger threshold / immunity said above, however in some cases it might take more than one parry to stagger an enemy. If an enemy is flashing with yellow / orange color it means they are nearing their Parry Stagger limit and one more parry on them will do the trick.

A Block is performed when you raise your defense but do not time it within the parry window. The block will deny the damage of the first melee attack you're hit by (except orange-glow attacks which cannot be parried or blocked), but will also stagger you and prevent you from blocking further attacks that may be coming at the same time of, or very soon after, the first one (the only exception to this is the Bulwark Class' shield, which can block consecutive attacks until its charge runs out).

Fencing is the highest parry class, which allows you to perform Perfect Parries much more easily as it gives a large bonus to the time window required to execute one, and also has almost zero cooldown before one parry and the next. Note that not all Fencing weapons have the same parry timing: for instance the Fencing Chainsword will have a somewhat tighter parry window compared to a Fencing Knife, even if both are Fencing. A Fencing weapon is the only type reliable enough to execute Consecutive Perfect Parries (explained below) against a large number of enemies. Fencing weapons have a smaller Block window, meaning that you either parry an enemy attack, or probably it will hit you instead of performing a Block, which happens when you time the parry well enough but NOT perfectly.

Balanced is the middle parry class, and allows you to perform both Perfect Parries and Blocks, but with a lesser window time-frame for both. Basically, it does everything, but does nothing really well. It's a viable choice and is perfectly fine for doing Perfect Parries against single Elite enemies / bosses or a few normal enemies, but won't be very effective against high numbers.

Blocking is the lowest class of parry and to my experience the worst. It prevents you from executing Perfect Parries (exception: the Heavy Class guns CAN perfect parry, since he has no melee weapon, but with a severely reduced parry window), allowing you only to Block enemy attacks but not parry them. It is fine against single enemies but you'll be in trouble against multiple ones or hordes with this one.


You can perform perfect parries on multiple incoming attacks, regardless of whatever animation your character seems to be performing (except when you're staggered / flinch by an enemy attack, of course). This will only work reliably with a Fencing class weapon, do not even try with a Balanced one because the parry window is not good enough.

As you know, a Perfect Parry will instantly kill normal enemies, and stagger larger ones after 1 or 2 perfect parries depending on their threshold. Performing consecutive perfect parries while surrounded by many small enemies, using a Fencing weapon, will result in your character parrying many incoming attacks at once, and instantly kill multiple enemies at the same time.

To do this, you need to have a Fencing weapon and be surrounded by many enemies which can be parried (so, not ranged ones). As long as you keep your attention up and press the Parry key each time you see an enemy attack you, before the attack lands, you can perform perfect parries on even 7-8-9-10+ enemies at the same time. This method can devastate hordes, especially of Tyranids, just remember to dodge Orange-glow attacks.

This method is high-risk because even one failed parry, against many small enemies, means you'll be hit and staggered, and all the oncoming multiple attacks will hit you, dealing severe damage. DO NOT perform Gun Strikes while doing this because they do NOT give you invulnerability and you will be mauled to death while the Gun Strike animation goes.

As of major update 3.0 of 26 Sep. 2024, ANY perfect parry in melee against small enemies will restore one armor segment.


When killing a Tyranid enemy of at least Elite class (the larger ones), if small Normal enemy units are present near the kill area, they will be hit by green lightning, which is a Neural Shock. This is because they're linked to the more powerful units with their mind. This shock can instantly kill or severely damage the smaller units, dealing a variable damage to each. Some will die, some will not, but all will be staggered.

This mechanic is very useful against hordes: executing / killing an Elite enemy surrounded by a bunch of small units will have roughly the same effect of a grenade, killing many of them instantly. This mechanic however will not affect larger units in any way.

You can cancel a charged shot or a grenade throw instantly by swapping weapons.
Suggested by: Tep

You can cancel a melee charged attack by parrying an attack.

Updated as of Patch 4.0

There is a way to skip bosses or Extremis enemies if you need to.

You need to enter a "transition" part of the map, such as an elevator or a double gate - any area that has a console to interact with and brings you to another area by closing a door or having you change elevation will generally work.

After you seal the doors / use the elevator, you'll get to the next area of the map.

Bosses and Extremis enemies will not follow you after this and they will be deleted / skipped.

NOTE: elevators will NOT WORK if ANY enemy is inside them, so kite them out or kill them before using the elevator.


In the final part of Inferno, the first Operation, you can activate gas pipes on one of the sides of the defense area, to trigger a huge explosion that will kill a large amount of enemies.

To do this correctly, first of all wait until the machine starts the process and starts summoning enemies to your position. After that, a member of the team needs to go on one of the side platforms and interact with the console that is glowing green. After that is done, another team member needs to interact with one of the consoles on the central area, left or right depending on which one of the outer consoles was activated, to trigger the gas explosion. You better wait for enemies to pile up on the walls and cluster up before exploding the gas, as it will not burn for a long time.

You will need to see from which side the wave is coming, so you can activate the correct one. Only one side can be activated at a time, and then triggers a cooldown after the gas has exploded. This process can be done up to two times, one for the first wave and one for the second wave of enemies.


In the final part of Ballistic Engine, the last operation in the list, you can interact with two consoles on the right walkway bridge (the one above the rail tracks, with a bent shape, not the straight bridge with the ammo crate, the other one) to call in additional trains. This is particularly useful to deal with the enemies assaulting the train carrying the bomb down below.

Calling a train when the enemy horde is swarming from below, so on the train tracks, will instantly kill all enemies in the train's path, and cut down their numbers by a huge amount. Two trains can be called depending on the side the horde is coming from. You can call trains again after a cooldown time.


Interacting with a Loadout Station in Operations and selecting your current Loadout from the panel will restore 100% of your ammo for all weapons.


Armory Data is found in those floating skulls that can spawn in many fixed locations in a level. The locations where they spawn are always fixed, meaning there are 3-4-5 depending on the level. Only one armory data Skull can spawn per level, so once you find it, don't look for more.

It can happen in some cases that the Armory Data may not spawn at all in the whole level. So yes, you think you missed it sometimes, but actually it might just have been bad luck with that level, and none spawned at all.

Guardian Relics also have fixed spawns, which are many more than Armory Data or Gene Seed ones. They follow the same rules, so in a level, even if it's very rare, there may spawn no Guardian Relics at all.

The same rules of course apply for the Gene Seed, which grants a +50% bonus to the mission XP. The Gene Seed will occupy the slot of a Guardian Relic, and can be dropped down for pickup only to swap it with a Guardian Relic.

The Armory Data is only gained if you finish the mission successfully. Finding it but then failing the mission means you will lose it. Same applies to the Gene Seed, which also is removed if the holder is knocked down once (not dead, just knocked down to be revived is enough to destroy the Gene Seed).

The Assault class' special move, Ground Pound, can stagger the Hive Tyrant boss and interrupt its wave attack. To do this correctly, you need to hit the Tyrant between the waves, or before it does the first wave. This is hard to time because if you're hit by a wave while in-transit to it while performing ground slam, so flying towards it, you'll be damaged and thrown to the ground. But still, it's possible.

The Tyranid "Tumor Warrior" can fire tumors on the ground that will generate a harmful poison area that looks like green barbed wire. These areas can actually be removed by shooting the central tumor of each area with any ranged weapon, or hitting it with a large area attack such as Thunder Hammer slam or Stomp of the Chainsword.

Suggested by Noctopus:
Another way to remove the tumors is to use the Iron Halo ability with the "AoE damage in 5 metres" passive active - this will remove the tumors by simply running into them.


When two Zoanthrope enemies spawn together, they will link to each other and grant a strong defensive shield to one of them at a time. This shield will periodically swap between one Zoanthrope and the other.

You might think this shield is indestructible because of the Armor icon that pops when you shoot it, but in reality it CAN be destroyed. It just has a very high health and will take several shots even from high-damage weapons such as Las Fusil or Heavy Plasma to do so.

Once removed the shield will not come back for a while, enough for you to deal with them more easily.


Chaos Sorcerers spawn with at least 3 defensive shields around them, which will be positioned to prevent damage from melee and ranged weapons. Attacking the shield in melee will immediately inflict the chaos corruption status effect on the player who attacks, spawning chaos illusion enemies, and make the sorcerer teleport away soon after.

However, these shields are weak to AoE damage, so a Frag Grenade or a shot from a Melta Weapon or a Heavy Plasma will often destroy all shields instantly, making the sorcerer vulnerable, and inflict no status effects. Heavy Stomp can work too but only if you're close enough and have the +50% Stomp Area upgrade from the related Weapon Perk tree.


Chaos Cultists (the smaller units the size of normal people) can be killed by simply running or dodging into them. You don't need to use attacks or shoot them if they're close to you: simply collide with them to kill them easily.
Suggested by: RatBallz