Bosses are AI Controlled tanks in Diep.io. All Bosses have 3,000 HP (which is Equivalent to the Alpha Pentagon) and give 30,000 XP to the player that killed the boss, there will also be a notification that displays for everyone in your server saying "The [Boss name] has been defeated by Player". Bosses do not appear in Maze.
The Fallen Booster is the worst boss in my opinion. It simply does not know when to give up trying to fight a player. This boss is strong against slow tanks but however is extremely weak against fast tanks with bullet builds like Fighter. Even a extremely fast Machine Gun at level 22 could beat the fallen booster with relative ease.
The Guardian, or as called by its full name The Guardian of the Pentagons is the first boss that was added. It is also very annoying like all the Bosses. The Guardian spawns a Horde of Crashers/Partisans that are controlled by the Guardian's AI, these Drones deal little damage compared to Overlord Drones and Disappear over time but however these little Pink Triangles can can eliminate almost all your health if you were to slam into a alot of them.
The Summoner is like a Necromancer combined with an Overlord. It spawns Necro-like Squares as its drones, however i like to think of them being like the Guardian's drones, they are pretty weak compared to Overlord's drones but however they Don't disappear like Guardian or Fallen Overlord drones.
Basically has the same properties as the Summoner but with more Crashers/Partisans and has 4 Spawners. It is the second Fallen Boss in the game and is grey like the Fallen Booster, however it is better than the Fallen Booster in my opinion because it survives longer.
The Defender is the only boss to use a different colored Ammunition, which makes it unique. It is also unique because it uses 2 Weapons that the other bosses don't, Auto Turrets and Trap Launchers. Its Auto Turrets are pretty decent compared to normal ones used by Auto Tanks. It is basically an Auto 3 Combined with a Tri Trapper except the body is shaped like a Triangle
How to defeat Bosses
Using an Overlord with the build 0/0/0/7/7/7/5/7 is a good choice since you have time to run away from the bosses drones. When the Drones are retreating back to the boss attack again and then repeat.
Bosses in TDM are easily defeatable since a horde of players could gang up on one boss and kill it, even if the boss has a giant amount of health it will still be defeatable.
The Defender is slightly harder to defeat than the Guardian or Summoner in my opinion because it has Auto Turrets that shoot very fast bullets, one of the ways to stop loosing health is if you dodge its bullets, also do not run into the Traps, as the Traps launched by the Defender deal alot of damage like normal Traps
The Fallen Booster is really weak but will kill alot of players in its short lifespan, so you have nothing to worry about unless the Fallen Booster randomly spawns near you and kills you out of nowhere.