Why John Wick Cut His Finger?

Throughout the movies we see that John just wants to be able to remember his wife. So by cutting off his ring finger, he metaphorically severed his last connection to his wife, and moved his devotion and fealty of that drive to grieve and remember to the High Table.

Why is John Wick called Baba Yaga?

He was later nicknamed "Baba Yaga", being further described as the man one would send to "kill the Bogeyman". His prowess was such that he once single-handedly killed three men in a bar with a pencil. Eventually, Wick fell in love with a woman named Helen.

What was the impossible task John Wick?

His superior, Viggo Tarasov, promised to allow John to quit if he first completed an "impossible task": killing all of Tarasov's enemies in a single night. Having succeeded, John retired and lived peacefully for just over five years.