I went in expecting it to be hard (one-shots on Youtube are as mythical for me as professional sportsmen breaking world records). My team was r5s Quake, Sinister, CMM, Sym Supreme and r2 Doom. Used Quake and Sym for the cosmic path (CMM for Aarkus). Then GM. Well, it took time to adjust to his fighting style, even though I watched enough videos.
First phase was relatively ok, but what really got me was the second one. Performing tasks was easy, but getting to the wounded phase proved to be extremely hard for me. Sometimes it would be just GM being extremely aggressive in infuriation phase and intercepting me like crazy. Sometimes it would be my champs doing things I didn't want them to do, like dashing forward when in fact I was blocking. The hardest thing for me ended up being his SP1. I could count a number of times I managed to evade it on one hand. I still don't know if it is my timing or lag, but I constantly got hit by it when dashing backwards. In the end Sinister proved to be a life saver, as I stopped trying to evade the SP1 and started to just parry it.
Third phase was easier, as I used only Sinister and it was easier to manage passive power gain from GM than enhanced power gain in second phase.
At some point I realized that my fingers were too sweaty and it was really messing inputs, so I put on gloves and did 7%-0% in one shot with Sinister. Now I wonder if it would make a difference if I wore gloves from the start...
Pull-wise, I got 6* CapIW from a 6* crystal (great, but I already have a sig 200 r5 5*), dupes of 5* Colossus and AA from Nexus and 5* crystal. Beast and dupe of BPIW from other two 5* crystals. Nothing fancy so far. Then I opened 4 cavs that came as a reward and got this:

Kind of made it worth it. Picked X-23 from Nexus (other two options were Man-Thing and Sentry).
Overall, I'm glad I finally did it and it now two 25% T5CC selectors away from becoming Thronebreaker.