Energy cores are objects and energy sources that appear in Splatoon 2 and Splatoon 3. They can be found in the Diaphragm Phase and Peristalsis Phase in the Octo Expansion, and in The Spirit Lifter: First Class in Return of the Mammalians. In the former, only one appears and is used to power an elevator, while in the latter, multiple small energy cores appear and are used to power switches that open bulkheads or doors.
They somewhat resemble Zapfish, but are small, red, and circular. HaikaraWalker confirms that they are Zapfish eggs.
In the Diaphragm Phase, the player must collect eight data points to release all the locks that surround an energy core. After all the locks are released, the energy core flies up into the next section. In the subsequent Peristalsis Phase, the energy core is placed in the middle of a moving platform and functions similarly to an orb. The player must attack the energy core to move the platform forward while also preventing enemies from attacking it; if the energy core sustains too much damage from enemies and has its health depleted, it explodes, instantly splatting the player. At the end of the Peristalsis Phase, the platform reaches a socket and is plugged in, allowing the energy core to power the elevator in the Spinal Phase.
In The Spirit Lifter: First Class, the player must use the Zipcaster to collect many small energy cores that power switches. There are three consecutive sections in which the player must collect energy cores and then step on a switch. The first two switches open a bulkhead for the player to continue, and the third opens the exit door.