i fought the gamma manticore. i got 16-17 (can’t remember, it was a while ago) high level rexes (lvl 150+, so probably overkill + imprinted) and one high level, imprinted yutyrannus. get in fight, get on yutyrannus, give courage to rexes, once it lands, rex rush it, then defend you, the yutyrannus and the rexes from the deathworms. keep doing this, and it dies in 5-10 minutes as long as you remember to keep courage-roaring the rexes with the yutyrannus. make sure you get saddles for all your creatures, and BRING GAS MASKS TO THE FIGHT. IF YOU DON’T, IT’LL KNOCK YOU OUT AND KILL YOU
Heres a tip FOR ALL THE PEOPLE SAYING YOU CAN FORCETAME IT IN THE ARENA- if u go into the bosses arena and forcetame it.... you'll be stuck there forever bc the boss gotta die in order for u to leave. :)
Bring around 6-7 or more rexs and when it lands everyone get around it and trap it. Deathworms will come and knock u back but just keep moving forward slowly so u dont get pushed out. Even when the rock golems come don't stop hitting it. Goodluck boys :)
When fighting the manticore a good strategy is bring in high level Rex's with good saddles and circle the manticore it then becomes pinned allowing you to kill it without it flying all around .... watch out for the poison it shoots at you though it will kill you off your mount like the poison wyvern ..