Remember not to use this card as a Tribute because this card may not fit the requirement of a Summon or an effect.
There's a simple combo using 1 "Evilswarm Castor", 1 "Evilswarm Kerykeion", and 2 of any Level 4 lswarm monster.
First, Summon either "Castor" or "Kerykeion", if you Summon "Kerykeion" first, return 1 of the lswarm monsters to the hand while banishing the other, then Normal Summon "Castor" through the effect of "Kerykeion". Then, use "Castor" effect to Summon the monster returned to the hand. Then, overlay them for "Evilswarm Ouroboros", "Number 10: Illumiknight", "Number 91: Thunder Spark Dragon", etc.
In a Steelswarm deck, you can Special Summon "Steelswarm Cell" from your hand, Normal Summon "Kerykeion", banish a monster and add "Evilswarm Castor" to your hand, Normal Summon "Castor" with "Kerykeion's" effect, Xyz Summon a monster and detach "Kerykeion" to the graveyard, then Tribute Summon "Steelswarm Longhorn" with the previously summoned "Steelswarm Cell" as the only tribute.
In this combo, you must Summon Castor with "Kerykeion's" effect. "Kerykeion's" extra Normal Summon is an ignition-type effect, while Castor's is continuous.
If your opponent controls at least one monster, and you control none, you can special summon "Evilswarm Mandragora" and normal summon this card for an easy Xyz Summon of two Xyz Material. Plus, if there are at least two Evilswarm monsters in your graveyard, you can banish one to return the other to your hand and use this card's effect to summon it, allowing access the Xyz monsters that require three Xyz material, such as "Evilswarm Ouroboros".