Mantis Lords

Behaviour and Tactics
It is recommended to initiate this boss fight after at least one Nail upgrade.

The Mantis Lords will not initiate battle until the player challenges them. At this point, a steel cage will prevent escape from the arena, with spiked pits to the left and right of the cage.

The battle begins against a single Mantis Lord. They'll execute one of three attacks, disappearing in a blur after each attack. The player must react quickly to dodge the attack, then strike the Mantis Lord before it vanishes. As the Mantis Lord loses health, the attacks become faster and faster. The best moment to heal is during the spinning blade attack. As is the case with most bosses, the Quick Focus charm is immensely helpful, despite its high cost.
 * Dash: appears on one side of the arena and dashes to the other.
 * Impale: appears above the player, attempting to impale them from above.
 * Blade Swing: perches on the side of the steel cage, throwing a spinning blade. Depending on whether the Lord is close to the ground or higher up, the blade's trajectory changes (the former demands an immediate jump, the latter will pass above the player at first, but can hit them as it returns).

Once the first Mantis Lord has been defeated, it will return to its throne. At this point, the two remaining ones will engage in tandem. The battle remains fundamentally the same, but the attacks come far more frequently and the patterns of the spinning blades change.

Once one of the two Lords goes down, the remainder of the battle becomes significantly easier, but since there is no visible difference between the two, it's impossible to focus on one over the other.

Trivia

 * Quirrel suggests upgrading the Nail before the fight.
 * Looking closely, there is a fourth broken throne in the room. The previous occupant of the throne is possibly the Traitor Lord.
 * The Mantis Lords are one of few bosses to have multiple entities attack the player. The others being the God Tamer and the Watcher Knights.
 * A lore tablet in the Mantis Village reveals that the Mantis Lords had some kind of deal with Hallownest, and that their end of the deal is to prevent the beasts of Deepnest from emerging. A gate opens from their throne room that connects to the Deepnest and a massive pile of dead beasts is seen nearby, with the Mantis Lords' nails sticking out of them.
 * The gates that fall down from the ceiling in the fight actually "fall down" from a rather thin floor. You can follow the gates up after the fight and find out that they simply just travel over all the scenery and ground all the way until you reach the next section.