I did that some years ago as well with backstab, scythe, reaping slash and death from above.
For all that wonder how this works: you need some slowing skills on you (for example from lancer) and additionaly use an "unstable etching" that you used to get from the etching introduction quest back in the days.
-Start the Etching Quest in Kaiator with the class you want to have this kind of experience with
-Do the quest until u are supposed to craft 20 x "Unstable Weapon Etching"
-Get a random weapon to use this etching on, equip the wpn and unequip every piece thats increasing your atk speed.
-Get a lancer with atk speed reduction glyphs equiped.
-You attack the lancer until you get a 10s "Catastrophe" Debuff (basically a Atk speed debuff on you)
-The lancer uses menacing wave, spring attack, leash for further atk speed debuffs
-You use the skill you want to use and enjoy the glory of the animation frame by frame.