I just finished my 5x Dagourmarche trial yesterday. I was lucky with the hydra pop items and finished the trial in 1 dyna session solo.
As for the strategy for the fight, it really is pretty easy. You should be using yuly for this fight. Falcorr works also but he's not as evasive as yuly and you'll end up using more pet food.
What I did for the fight was pop the NM and send your pet in. Wait until he spawns the wyvern. Usually takes about 5 secs. Engage and start TP'ing. Wait until he starts casting for his avatar and ruinator while he's casting. Takes a while for him to cast so you'll be safe. Snarl and that should cement hate on your pet for the fight. Don't worry about spamming your fight command as you'll be doing most of the damage. Only thing you need to watch for his Astral flow which will do 600-1000 dmg. He also uses grim halo which can do 400-500 dmg. Have 5 steps comming into the fight and heal yourself right after astral flow in case he uses those 2 moves back to back. Spam ruinator and snarl when it's up and he should go down in 4-5 mins. You might end up using 2-3 pet food during the fight.