My college once wonder how I can memorize so many mechanics and I was like what? Only then I notice since I did back then a lot of Duty Rouletts I hat learend many many mechanics of Trials dungeons etc. Thing is, reflecting back on then I notice a lot of attacks that are Instant kills or very close to especaly in later stages of the game... but there is no way of knowing the first time you encounter them.
And a game mechanic which biggest chalange it is that you do not yet know what it will do... is not good game design.