As for why, well, there are a lot of reasons: lots of chase cards in this set, alt art galore, and lots of high-value singles
When a creature card (or its copy) is on the stack, it is a spell
100-Card Singleton: Your deck must contain exactly 100 cards, including your commander
Legendary Creature - Human Bear Color tag templates(None) Trostani, Selesnya's Voice Whenever another creature you control enters, you gain life equal to that creature's toughness
Some might say your opponents creatures are the best sacrifices, forming the entire crux for steal-and-sac commanders
Two mana 3/1s tend to play pretty well in aggro decks, and thats what you get up front here and then you have the option of moving the Equipment to other stuff like if you really want your token to be a 2/2, or if something else can benefit from the stat boost