Areas Overview

Nuclear Throne has a total of 7 main areas, with an 8th added in loop.
Every odd-numbered area has 3 levels with a boss fight at the end of each.
Every even-numbered area has a single level and is transitional.

There are also 7 secret areas, with an 8th added in loop. This brings the total to 16 unique world/places, each with their own theming, music and enemies.

Levels end upon every enemy being killed, or a secret area is entered. This will spawn an exit portal which will suck the player in if they get too close. Every portal entered will increase the difficulty which raises the odds of more enemies spawning, as well as advancing the possible weapon pool drops.

Portals

Portals function as level exits and will appear once every enemy is killed. Their placement will always be over the corpse of the last enemy killed, though this can be difficult to predict in crowded levels. Vans and props do not need to be destroyed to trigger the portal, however if either are destroyed right after the last enemy is killed, the portal will instead spawn in their location.

If secret area conditions are fulfilled after the level is already cleared out, it will result in two portals. Entering either will result in the secret area.

Normal	Vault	IDPD

Portals will suck the player in, with a stronger pull based on proximity. If the portal is touched at all this will cause the level to end, even if the player manages to escape its pull such as with Fish's Throne Butt.

Portals opening will break any nearby walls or props to be destroyed, which can include hazardous props. It will also cause any chests and rad canisters within proximity to burst open.
While portals are active all pickups and rads will automatically be pulled towards the player regardless of proximity. Any pickups and rads that come in contact with the portal will automatically be collected.
Weapons that are close enough to the portal will get sucked in and will be at the next level's spawn.

When inside the portal, the player's sprite will be changed to their hurt animation. During this brief period before level end they are invulnerable to any sources of enemy damage, but are still able to self-damage through blood weapons and certain character actives.

While right outside of the portal, there is a brief period in which the player has their hurt animation active but will only gain invulnerability to damage sources that respect player iframes. One of the notable damage sources that does not respect player iframes are explosions, meaning that if the portal causes a nearby car prop to explode it can kill the player right before reaching the portal. (Boiling Veins will grant full invulnerability to explosives in this specific state, as it makes explosives respect iframes.)

A small audio cue will be played when there is only one enemy left alive in the level. This can play multiple times if additional enemies are spawned before spawning the portal.

Rare Bug: If all the enemies are killed but the exit portal does not open, that means an enemy got stuck inside of a wall without dying. If this happens, walk the levels perimeter to try to find them. (Melee weapons work best here as they can hit into walls.)

In even rarer cases enemies can escape the surrounding walls completely and can walk freely out of bounds. They will take 100 damage every 3 seconds in this state. The exit portal will always spawn in-bounds for the player.

Giant Portal

On 7-3 and 0-1 giant portals will spawn in the place of normal ones. They will suck the player in regardless of distance, unless if behind a wall on 7-3.
Being sucked into a giant portal puts the player in the semi-invulnerable state mentioned above, although there are no typical hazards after the fight ends.
The exception to this is for Loops 4+, where Popo Freaks can respawn even after the fight ends on 0-1. While being sucked the player is immune to their contact and bullet damage, but not their explosive grenades, unless if running Boiling Veins.

Entering the 7-3 portal specifically will uncurse any currently held weapons. The 0-1 portal will not uncurse weapons despite looking the same.

Looping

This section is a summary of various other pages.

The start of the game is commonly known as 'preloop', Loop 0. Upon fulfilling the condition to loop, the player will loop past 7-3 back to the Campfire, 0-1.
Areas will repeat normally throughout loop but will be significantly more difficult to progress through. There is no limit to how many times the game can be looped.

Here is a brief overview of every change made in loop:

• Enemies:
• All main areas will include 2-3 enemy types only seen in other areas.
• Elite enemy variants will become more common.
• All transitional areas now include unique bosses.
• IDPD and Vans will spawn during most levels partway in.
• IDPD spawns can include Elite IDPD, which are more numerous and common in Loop 2.
• Starting from Loop 3, all IDPD will be replaced by Popo Freaks instead.
• Secret areas will not have additional enemy types, but most will have IDPD spawns.
• Enemy Behaviors:
• Most enemies now have a chance to spawn in clusters (groups) on level generation.
• Each loop increases the odds of spawning in a cluster, as well as the quantity of enemies. (+4 for Loop 1, +5 for Loop 2, so on.)
• All but one boss will have specific attacks scale by loop, becoming increasingly more dangerous.
• Enemies will also have their HP scale by loop, with bosses increasing at a much faster rate.
• For Enemies: BaseHP * (1 + (1 / 20) * Loop)
• For Bosses: BaseHP * (1 + (1 / 20) * Loop) * (1 + (1 / 3) * Loop)
• For Big Dog: BaseHP * (1 + (1 / 20) * Loop) * (1 + (4 / 5) * Loop)
• Props always have the same HP, exception being Proto Statues.
• Weapons:
• Gold weapon and ultra weapon variants are all added to the drop pool.
• Pickups:
• All pickups and rads will reach their despawning phase much sooner, scaling by loop. (Specific details coming soon!)
• Vaults:
• Loop-specific crown options, regardless of loop.
• Proto Statues will additionally spawn on 1-2 and 7-2.
• Proto Statues gain +12 HP per loop.

Every main area in loop will also have a modified spawn pool that has a chance of replacing the original one.
The enemies in the loop spawn pool are typically more difficult to deal with, and will include enemy types from other areas.

Each enemy separately rolls the chance of pulling from the loop spawn pool instead of the normal spawn pool, with the chances of the loop spawn pool being pulled from increasing with every loop. The following table shows the odds of this happening.
A 100% chance of replacing the loop spawn pool is never reached.