so guys i was making a deck and i found these two cards evilswarm kerykeion and constellar sombres their effects are exact same plus even their picture looks almost similar as if they are siblings..... and one more thing even their atk and def are kindof same its switched

Makes sense to say evilswarms are dark counterparts of Constellars...

Evilswarms are kinda infected versions of other "Duel terminal" monsters. Like:
Daigusto Falco = Evilswarm Hraesvelg
Gemknight Emerald = Evilswarm Heliotrope
Jurrac Titano = Evilswarm Salamandra

Just to mention a few.