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 "Kerykeion" is Summoned 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 the effect of "Castor" 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, "Steelswarm Cell" can be Special Summoned from your hand and Normal Summon "Kerykeion". Banish a monster and add "Evilswarm Castor" to your hand. Normal Summon "Castor" with the effect of "Kerykeion" and Xyz Summon a monster. Detach "Kerykeion" to the Graveyard, then Tribute Summon "Steelswarm Longhorn" with the previously Summoned "Cell" as the only Tribute.
In this combo, "Castor" must be Summoned with the effect of "Kerykeion". The extra Normal Summon from "Kerykeion" is an Ignition-type effect, while "Castor" is Continuous.
If your opponent controls at least one monster, and there are none on your field, "Evilswarm Mandragora" can be Special Summoned 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, one can be banished 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".