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 ..
Brany 2 of my best wyvern( 1 fire and 1 lightning). Both are over Lvl 100. My best rex (once again over Lvl 100). All have over 5,000 health and over 1,000 attack. And don't forget the yuter with over 1,000 attack and just to give them extra power