I believe ancient guardian was a joke boss since dont starve together released for you can get him stuck 9.99/10 times. For once, show him some love!
What cheese strats are there?
Well, he does get stuck on tombstone (since DS if I am not mistaken). When you are forced to use one tombstone (very rare scenario, since there is a reliable cheese strat described next) its actually cheeky and challenging, but if two of those are close to each other - you can permanently get him stuck.
The other one is that by getting yourself between the void and pillar he will never reach you, as long as you keep hitting back. For extra swag you can just count the damage you do and knowing his max health predict when is it time to rellocate him so you dont risk loosing items to the void.
Perhaps the easiest fix of second strat (the cheesiest) would be just adding one tile around the arena or moving them one tile closer to the center? Kiting around pillar might be somewhat cheesy, but very tricky and interesting.
On tombstones its a bit more cheeky. I suggest making tombstones hammerable for stone.