Given most elf decks rely on mana generation to get value creatures on the board, having Nissa on your side isn't a bad shout
For the most part, Wizards have triggers that draw cards or annoy the opponent by bouncing things, but Anathemancer goes straight for the heart for a ton of damage
7 Culling Ritual Mana rocks, such as Sol Ring and Mind Stone, are so ubiquitous in Commander that many are considered auto-includes regardless of deck type
Nekusar is Grixis, meaning he has the right colors for a deadly and flexible Zombie deck with all the right removal and card draw effects to dominate any game
Whenever King of the Oathbreakers or another Spirit you control becomes the target of a spell, it phases out
Yes, development spends a lot of time trying to figure out where a set will take the metagame, but by that point the design is already handed off