Summoner

The Summoner is a square boss that was added on August 17, 2018. It looks like the Necromancer, but is much larger and continuously spawns drones while attacking.

Design
Summoner has a yellow square base and four Underseer drone spawners around it.

Technical
Summoner has low speed and health and summons sunchips at a very fast rate. Its sunchips have low health and penetration, but decent damage and speed.

Spawning
Summoner can spawn on the death of Xyv Wdtcfgzsezgk, or when Square Sanctuary dies.

Countering
Summoner is one of the weakest bosses, so killing it will unlikely be a problem. All tanks with high penetration and RoF can easily eliminate the Summoner, as you will be dealing high damage while penetrating most sunchips. As the focused-fire tank, try to keep a medium distance while spraying some bullets in the direction of incoming sunchips. Hexa Tank branch can also eliminate all the sunchips and kill the boss pretty easily. As a minion tank, you should consider keeping your minions between you and the Necromancer, so that they will absorb most of the sunchips. As an Engineer branch tank, try to create yourself a fortification from pillboxes and periodically launch your pillboxes into the boss.

If the boss spawned from the death of Xyv Wdtcfgzsezgk, you have two options to go. The first option is to quickly eliminate Guardian, and then apply the strategies above on the Summoner. Another option is to focus on killing the Summoner first due to its low health and then retreat from the Guardian and Defender.

Trivia

 * This boss exists in both Diep.io and Arras.io and Woomy-Arras.io and its the only boss with this ability.
 * And this is the only in-game boss that uses Summoner Squares-Necro drones to attack.