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Co-Op Overview

In the vanilla version of Nuclear Throne, local co-op play allows for two players to play a run together at the same time. This differs from the mod Nuclear Throne Together (NTT).
NTT allows for 2-4 player co-op and online functionality with the option of mods, but only works on PC versions of the game and does not give achievements. There is a Steam beta branch that does not require an external download (ntt_development), but for stable/other PC versions it must be downloaded from the actual mod page.

Co-op mode uses the same mechanics as normal mode. The only different mechanics is how death works, and different ultra mutations.

In order to use golden weapons or crowns on vanilla co-op, enter the normal menu first for a singleplayer run and select the golden weapon for both characters being played as. For crowns, select the desired starter on whichever character Player 1 will select. Whichever is selected will be applied during the co-op runs.
(Selecting Golden Frog Pistol as the starting weapon will transform that character to Frog on co-op as well).
For NTT, these methods can be done, but the '/bwep', '/cwep', and '/ccrown' commands all work as well.

For B-Skin selection, using the weapon swap button will swap between skins in the co-op menu. (scroll wheel or spacebar on KBM setup)

Hardmode co-op was only added on vanilla NT for 2021 openbeta forwards, meaning it cannot be played locally in older versions. For NTT, the /hardmode command can be used to enable/disable it.

Run Mechanics

On local co-op the camera will focus between the two players, which means that both need to stick near each other constantly. Only when one player dies is the other temporarily given free cam.
On NTT each unique session gets their own free cam to control, meaning that players can clear different parts of the level to complete it quicker. However if a partner dies off-screen, it will take longer to retrieve them when reviving is on a time limit.

What is shared between players:

• Rad meter. Collecting rads helps both players at the same time. This includes using it for ultra weapons.
• Mutations. There is only one set of shared mutations, so picking mutations may take some communication for what helps both players the best.
• Crowns. Only one crown can be ran at a time still.

What is different between players:

• Weapons. Each player has their own two weapons. If they wish to trade weapons it needs to be done by swapping with a weapon on the ground.
• Ammo and health. Drops and chests will only apply to the character who collects them, which may put the other player in a vulnerable position.
• This can be mediated by the co-op ultras which offsets these issues.

Only one character needs to enter the exit portal in order to leave the area.

Players cannot normally friendly fire each other, but there are exceptions to this. (More details later)

Death Mechanics

Both players are capable of reviving each other at the cost of HP, meaning a run will only end if both players fully run out of health.

If one player takes a lethal hit they will temporarily die but have a ghost sprite in the location they died at. If the ghost sprite is touched by the other player they will automatically be revived and the player will 'gift' them half of their current health, rounded up. If the dead player's max health is below half the health the alive player has, the alive player will simply gift the dead player to their full health.

On death the text 'FAINTED' will appear over the dead players health bar as a countdown will begin ticking behind it. This countdown lasts around 10 seconds, and once it runs out and the player has not yet been revived, it will begin to damage the alive player at one damage per second.

When the alive player is only at 1 HP (without Spirit) and they try to revive a player, they will instead die in their place. There is a cooldown of 1 second before being able to be revived again to avoid getting stuck. As the revive countdown takes 10 seconds, the two players can continually swap between who is alive to reset the countdown until a health pickup is found, albeit in a very vulnerable position.

If Chicken takes a lethal hit she will enter her headless state before entering her fainted state, meaning that she cannot avoid losing max health. She cannot revive another dead player while headless.

Dead players drop their weapons but will be automatically picked back up upon revival. The exception to this is if the alive player gets sucked into the portal; both will be brought to the next level but the dead player will no longer have their weapons, leaving them vulnerable when revived.

Mutation & Passive Mechanics

Coming soon to a Wasteland near you!

Ultra Mutations

Vanilla NT only gives the options between two ultras that are unique to co-op, being Gun Bond and Blood Bond. NTT has commands to allow for the usage of character-specific ultras.

Co-Op Ultra Mutations
Blood Bond	"HP Pickups Are Shared" The Ultra A co-op ultra, any health pickup/chest now will apply to both characters.
Gun Bond	"Ammo Pickups Are Shared" The Ultra B co-op ultra, any ammo pickup/chest now will apply to both characters. Whoever picks up ammo will have the drop chances apply to them, and then that ammo type will also be shared with the player. However opening an ammo chest will give ammo both specific to each players' primary weapon independent of each other.

Within NTT using the '/ultras all' command lets players choose between either taking a co-op ultra, or each character picking one of their own ultras. Both a co-op and a character-specific ultra cannot be run at the same time. If two players are running the same character, they cannot pick both ultras but will only get the choice to take one.

Similar to passives, some character ultras will apply to all characters while others will only apply to their specific powers. This guide will later include these interactions.