Best way by far is bringing as much lightning wyverns as possible. (Most I ever brought was 12 you could probably Cram more into the arena) Make sure you hatch them from lvl 190 eggs and breed them. Bring hundreds of stimulants and put them in the wyvern you will ride. Bring a gas mask or two, an assault rifle with a couple hundred bullets. A rocket launcher with at least 12 rockets. Medical brews and water and food. When you first load in get the wyverns to attack the manticore and pump the stimulants on your wyvern when it’s torpor rises. Be aware it will knock out your wyverns very easily. I brought 9 lvl 250 wyverns into the gamma manticore and the manticore knocked out 7 of them and killed one of them.

More Manticore Encountering Tips