Bring a snow owl and heal the ossi if it's health gets low. Remember to bring med brews, trust me you'll need them. Focus on the icicles first, then get the small dinos. When tranqing it, do it while on a desmodus. When it's dazed fly close and jump of desmo right on its back and mount. Takes a bit of time to tame but don't give up, you'll get one.