Most planeswalkers also have an ultimate ability, usually marked by a large negative number
P/T Number 551 Language English Legal Formats Commander, Historic, Legacy, Modern, Vintage Not Legal Formats Alchemy, Brawl, Competitive Brawl, Pauper, Pioneer, Standard, Timeless Rulings (6/16/2023) The last ability of Nazgl lets you ignore the "four-of" rule
Krark wore the thumb around his neck along with his other good luck charms until the end of his days (which wasn't very long, as his journey got him executed for heresy)
Four toughness is incredibly relevant because it allows this to survive Lightning Bolt and much other cheap interaction, and the threat to adapt it later makes it relevant when you have some extra mana
This lets players empty their hands and use more spells than they have mana for
Timeless Witness