Eileithyia is a boss that has a chance to replace Tartarus in Easy Company. She will also appear from the Airlock, but does not hatch from the Giant Egg. She is a bloated flying creature that can change color to indicate what she will spawn. If left uncontrolled, she can get moving at surprisingly high speeds.
Eileithyia is fought in a completely different manner than Tartarus. In Veteran Mode or higher, 2 Brain Bugs spawn at the beginning of this fight. For the first few seconds of the fight, she is invulnerable. However, she can still be affected by skills. It is important to stun her during this period, the Assault's Charge or Demolition's Sap works best. However, self destructing an Engineer's disruption tower works as a last resort. If allowed to escape, Eileithyia will fly about the battlefield at high speeds, pausing only to lay eggs. It is helpful to Laser Designate her early so the team can track her movement.
The color of her body signifies what type of enemy will hatch from her eggs. When heavily injured, she will enter a regenerative state. If not killed quickly, she will fully heal, and resume laying eggs. Eileithyia can repeat this cycle up to 5 times. Simply hammer her with high powered weapons and skills, with one character either using a Flamethrower MK-3, Shotgun, or AoE skill to kill the Zombie Eggs she lays. With the combination high firepower and stuns, she should fall with ease.
Eileithyia will spawn along with a Tartarus on round 10 of Survival. It is important to note that if not killed within the allotted time, she will morph into a dangerous Queen. This Queen will be much faster than in Easy Company, and if Eileithyia morphs, the game will almost surely be lost.
Eileithyia is one of the few flying bosses, and the only true flying boss on Easy Company. This means she is unhindered by terrain and will often fly over sight obstructions or briefly over impassible terrain. This can be problematic given the large amounts of debris outside the Airlock gate. She is also immune to ground only weapons, ie, the Flamethrower MK-3. Stunning her is the only real counter to this, as flying is irrelevant if the unit is immobile.
Eileithyia will change color and lay a clutch of eggs. Her body color will determine what the eggs will hatch into, and will give the player an early warning. Several players should stick to using Flamethrower MK-3s and kill as many eggs as possible. The rest of the team should focus on killing Eileithyia herself.
Hatches into Gargoyles, easily sprayed down by the UA GPR-12, can be painful if they mass a single character. Sonic Traps, 590A5 Combat Shotguns, and MP9A2 Sub-Machine Guns are also highly effective. In Nightmare Mode, yellow eggs can also hatch into Wraiths.
Releases Banelings, very dangerous, with high splash. Best to move back a safe distance, and ready stuns or other slowing techniques. Characters with Reactive Armor can absorb blows for their allies. In Nightmare Mode, blue eggs can also hatch into Beastlings. However, blue eggs are 40% weaker than other eggs.
When significantly injured, Eileithyia will try to to heal herself. Now is the time to unload. Combine fire from high damage skills, and stun her. If she escapes to beyond your sight range, it can spell trouble. If allowed to regenerate Eileithyia returns to full health. She can only do this five times before she is unable to further regenerate.
In Nightmare Mode, if a player runs underneath Eileithyia, she will drop a large number of parasites. Given the Parasites low threat value, it will be incredibly difficult to target them and they will need to be killed by area-of-effect skills.