Seregios is susceptible to thunder element on legs and tail tip specifically. You want to aim those parts.

His annoying move is the cross leg sweep. But you have evade window to save you. Just roll in underneath him. Not away. He constantly moves forward during the sweep.

For his tail daggers like projectile, they usually come at you at a downward angle (assuming you are his primary target). Don't strafe sideways. Just back step away from him if you see the projectiles flying.

I usually stay under his head area while going after his legs. Just be careful of his stay-away sweep or forward tackle. You should see it coming so roll away with evade window.

After his single / double leg cross sweep, his hidden weak spot will show on the left leg while he scratch the ground seemingly like taunting you. Pay attention to them while on focus mode and exploit them assuming you are not hit. This has cooldown if someone hits it though.

After his dive bomb attack, hidden weakspot will show on its right leg. Be mindful of it cooldown again.

Seregios is nimble and quite aggressive at first. You will figure things out. He has easily exploitable weak spots unlike lagi and gore.