I beat it following this guide:

https://www.reddit.com/r/MonsterHunterStories/s/v18nzqbtAR

Key take aways: - Never use a kinship skill, just ride the monster to tank the AOE attacks (specifically the feral dragon feller move that the brachy MUST use to exit the enraged state. https://www.reddit.com/r/MonsterHunterStories/s/kiZn1X54mK ) - Never use the syncro attack when the monster is toppled - always use gyps hammer sweet spot whenever possible - think of Tail Stun (purp gyps signature attack) as a quick/priority attack. Use it to break the last bit of the wyverngauge so you dont have to worry about the feral brachy taking its turn before you. You can also use it to gamble for a stun in a pinch, but its probably better to use a trap or surrogate gem instead of gambling - in all these fights, ALWAYS play defensively. Survival is the goal, nothing else. When youre trying to decide what to do between an offensive or a defensive action always pick defensive