Let me start with saying my golden disclaimer that I last played back in MHWorld around when Alatreon got released. I even bought Iceborne with a friend (I think I bought it for him as well) but sadly he eventually got a family and I don’t wanna take the family time from him so we basically ditched the game. I didn’t play the MH series where Seregios got released and this is my first series encountering the monster.
So let’s begin with what I know so far.
Whether I’m solo or in a group hunt. I usually start with a basic max charged slash (CS) then lock on to his head for good measure right before the slash hits. Then, I immediately roll-over to the side about twice or until I know I’m safe.
Now for solo hunts. There’s two things so far that it does when I do the sequence above.
#1 either it leaps and glides in the air then dives twice.
So what I currently do with this is on the fourth side evade (OMG I initially wrote third side evade and did it in-game then got whooped by Seregios 
so yeah I guess this confirms the 4 side evades puts you in a safe spot) I immediately tackle then charge up my strong charged slash (SCS) up to max and retarget my lock onto the hindlegs (I read somewhere that his hindlegs are very fragile and can easily topple it). With the right level and grade of equipments, this strategy immediately topples Seregios. But lower level and grade of equips can be risky because you are open on the next quick attack in succession which this monster seems to be known for.
#2 it prepares to attack then throws his blades towards your original location and then tail swipes (I think) afterwards.
What I currently do with this is still side evade but only three times. But instead of a tackle, I immediately charge a basic CS because at the start of charging I think Seregios is already doing the tail swipe. So just 1 charge here then release lock on or relock onto wings so you hit the wings instead of his head initally that is out-of-reach. From here, I can usually side evade and be safe on the next quick attack.
The glide into 1 dive is sort of easy but I find it impossible to max charge a true charged slash (TCS) so instead I just go for an SCS at the moment. Let me know if there is a trick to squeeze in a TCS.
Other attacks, I’m still learning for now . I just wing it and hope I don’t get hit 
. Haven’t mastered the hitboxes, openings, and timings yet so any help would be appreciated. Mastering new monsters in a 75-second hunt and hp management on the verge of emptying my bank account doesn’t really help .
So in case any hunter recognizes me, I am currently getting carried in 10* hunt-a-thons not gonna lie . I mean I can handle 8* Seregios. But 9* and 10* requires me to play flawlessly and hit all of my max charges. Honestly, I just recently under-performed in a hunt-a-thon and made us fail the 10* Seregios apart from the one hunter leaving the hunt because he might have noticed me missing those charged slashes . Fortunately, the reattempt was successful with me still honestly not doing great. So I apologize for that. And I already sold my soul to the devil. I might as well reap the rewards by greeding the 10* Seregios. But don’t get me wrong, this is like my 3rd or 4th Seregios Hunt-a-thons with two 8*, two 9*, and one 10*. Let me tell you that I carried my weight during those hunts until the last one. Not every day is my lucky day. And this post can hopefully help me master this son of gun Seregios .
In group hunts, I think going at the back is the safest. I’m trying the side and I get punished if I don’t read the attack moves correctly. And yeah any tips and tricks as well during group hunts is appreciated.
Last but not the least, blocking the roar with tackle is key to my solo hunts. You can then max charge an SCS (not sure if TCS is possible due to next quick attack) safely and evade next quick attack. So if I miss blocking it, I immediately escape my hunt .
I have attached my current equipment set and skills. Don’t worry about the raw power decreasing affinity by 5%. It’s just 5% anyway so affinity still pretty good at 20% currently and 25% at G10. I get +60 attack power and Lv 2 concentration as a trade-off (raw power decreases 40 attack power from critical strength) which means more up time in special skill. I’m currently thinking of getting Bazelgeuse greaves with +550 attack power at Valor lv 2 but it only activates when a monster roars. There are times when a roar gets cancelled by a staggering attack so I figure that it is a conditional skill and not always active. I might consider it but I am focusing Bazelgeuse vambraces at the moment for my critical ferocity build. I currently can attach another Timed Charger skill from a driftgem which can improve my Seregios hunts but it would require me to spend Base Defense tokens for the armor refining parts. I am currently prioritizing earth crystals, carpenter bug, wyver scarcestone, etc at the moment for the base defense tokens especially due to armor refining parts being available in daily quests. So I need about 2 days as of this writing before I can add another Timed Charger skill with +10% attack power increase .
P.S.: Tips will be greatly appreciated but I did try Thunder DB and it was easier to slay Seregios. My Thunder DB build will be available for a couple of days or weeks probably by hunting Barioths, Khezu, Goss Harag, and Astalos.