Not really a level but as an achievement collector in World of Warcraft, I try to make all of them during an expansion.
There’s a pet battle system which is basically a Pokemon game inside the game.
During the Legion expansion and more precisely the last patch introducing Argus, you had legendary pet bosses to fight.
The NIGHTMARE!
Even if I already several hundreds of pets by the time, there were some of the bosses who requested a specific pet, that could drop with a very low drop rate (or buy for tens of thousands of gold) WITH a specific set of statistics and then you needed the fight to happen not with a strategy but with luck.
Boss hits you with a crit in first? Start again!
You miss or do not hit critically? Start again!
And this was throughout the whole fight!
It was the one and only time I was so enraged by the game I nearly cancelled my account!