Who's your favourite skill check boss in a Soulslike?

Genichiro in Sekiro, Viper in Khazan, Gascoigne in Bloodborne - skill checks in soulslikes are used quite often to gatekeep the rest of the game until you learn whatever it is the game wants you to learn.

Gascoigne wants your to adapt to the visceral, fast-paced, aggressive combat of Bloodborne. Genichiro tells you to parry or fuck off because he will be the least of your problems come around the mid to late game. Viper is in a similar boat, adding tenacity to the mix because the fight is ungodly long that early in the game because your damage output is laughable and he hits like a truck.

Who's your favourite skill check? Which other skill checks even exist in other soulslikes? Is Flamelurker in DeS a skill check? What about Capra Demon?