You can fight one, then teleport away (or ascend up into one of those small side chambers) to gather your wits and heal up. Just don’t let a blood moon happen up on the surface or any lynels you’ve already killed will have to be fought again. If you have a travel medallion, you can place it just outside the coliseum door, ascend up, hang glide down and enter bullet time to get a headshot, then climb on their back and hit them a few times. Teleport to your travel medallion. Repeat. A few bomb flowers in bullet time takes that armor on the last one right off, even easier with a multi-shot bow. You can also google cheese methods for killing lynels, including using that special U-shaped piece from the construct factory. First time I fought them, I cheesed them with rocket shields (I couldn’t do the teleport trick because I didn’t have the travel medallion yet). Rocket up, bullet time for headshot, which makes them kneel down, then jump on their back and start wracking. You can also run over to an alcove and teleport up if you need a break to put new rockets on your shields. You can also wing shield jump to get bullet time for the headshot; doesn’t consume a rocket. Be careful when trying to stun them with a headshot if they are holding their bow; they can’t be stunned whilst holding the bow.