Polygons

Polygons are naturally-spawned, uncontrollable objects that dot the arena. Unlike tanks, they do not have their own weapons and can only use body damage to defend themselves. Most serve as an experience resource for players, with the total experience of the polygon going to the player who destroyed it. Polygons will regenerate health if they are left unharmed. Polygons slowly drift and will harmlessly repel each other, although damage is dealt to players if hit. Pink Triangles, unlike other polygons, follow the player to defend the pentagon nest

Yellow Squares
Main Article: Yellow Square The Yellow Square is the weakest and most common type of polygon in the game and as such gives little experience, but it is useful for tier 0 players, as a way to farm experience. Currently it drops 10 experience points, 20 points in Domination and 30 points in Mothership. Necromancers can convert yellow squares into drones by bumping into them.

Red Triangles
Main Article: Red Triangle

The Red Triangle is stronger than the Yellow Square and the second weakest, but weaker than the Blue and Alpha Pentagons. Currently it drops 25 experience points, 50 points in Domination and 75 points in Mothership.

Blue Pentagons
Main Article: Blue Pentagon The Blue Pentagon is the second strongest polygon in the game and is regarded as the best source for experience. Tier 0 tanks will benefit greatly if the opportunity arises to destroy one. It currently drops 150 experience points, 300 points in Domination and 450 points in Mothership.

Alpha Pentagons
Main Article: Alpha Pentagon The Alpha Pentagon is the strongest polygon in the game, taking many hits to kill even for the strongest players. Killing one rewards up to 3000 experience, making it the largest possible source of experience in the game. Alpha Pentagons only spawn in the Pentagon Nest.

The Pentagon Nest
Main Article: The Pentagon Nest The Pentagon Nest is an area located in the center of the arena. It has a high concentration of Blue Pentagons and Alpha Pentagons, as well as Pink Triangles that target players.

Pink Triangles and Big Pink Triangles
Main Article: Pink Triangles The Pink Triangles often come in swarms and will seek players. They spawn in the Pentagon Nest, but will continue to follow the player until either the triangles or the player are destroyed. They have two sizes: Small and Large.

It should also be noted that turning invisible with the Manager and Stalker classes will cause the Pink Triangles to immediately stop their targeting [from you], or lock on to another close player.

Necromancer Square Drones
Main Article: Necromancer

The Necromancer Squares are square drones that are under the control of a Necromancer. They are orange in FFA mode, but take on the color of their owner in the Mothership, Domination, and Team DM modes. The tank touches and "infects" yellow squares to become the it's drones. The power and quantity of these square drones depends on the stats of the tank.

Overseer/Overlord/Manager Triangle Drones
The Overseer, Overlord and Manager's Triangles behave like the Necromancer's square drones (controllable but will otherwise seek out polygons and enemies). They are spawned directly from the tank with a maximum of 8 triangle drones at any time. Overall, these   drones have higher health, speed, and damage compared to those used by Necromancers.

Hybrid Triangle Drones
The Hybrid Triangles are   drones somewhat similar to the Overseer, Overlord, and Manager's Triangles, but are stronger and non-controllable. A Hybrid can spawn maximum two Triangles. Like other drones, they seek out and destroy enemies and polygons.

Guardians
Main Article: Guardians Guardians exist in Team DM and Domination within the team base to keep the enemy from getting too close. They also defend the Mothership in Mothership mode. They appear to be the same colour as the team they are defending.

Trivia

 * Previous versions of diep.io had a health bar under each Necromancer Square Drone. This was later removed.
 * Player's Drones destroy polygons and nearby players when not given a command. When there is nothing to destroy, they will form a passive shield around the player.
 * After the June 15th changelog, when you upgrade to Overseer and above, Bullet Penetration, Bullet Speed and Bullet Damage will respectively become Drone Health, Drone Speed and Drone Damage. For Necromancers, Reload will also change to Drone Count.
 * Like their tank, Drones will be the color of their team, which is sometimes the only way to distinguish the manager's team color.
 * Although size seems to affect the points a polygon gives, spawn guardians are immortal.
 * The points given by the polygons don't decrease as you get bigger, contrary to many people's belief.