The best part is that people often won't tap and use stuff if they think Nahiri is just going to exile it, and often creatures won't get used
Most of the cards that make Legacy expensive are the same cards that make Modern expensive: Snapcaster Mage, Liliana of the Veil, Misty Rainforest, etc
Otherwise, Ive seen many players build Svella as a land destruction commander
For one green mana, Helix Pinnacle is a card that can completely change your objective and approach to winning a game of Commander
3 different pack arts are available
Youll still need a little graveyard hate like Scrabbling Claws or Withered Wretch in order to take out things that are inconvenient (like Ulamog, the Infinite Gyre), but then its time to Bring Out Your Dead with Rise of the Dark Realms, Liliana Vess, Sepulchral Primordial, Havengul Lich, and Geth, Lord of the Vault