Given Simic colors propensity for big mana, Xolatoyac allows you to go for broke summoning your creatures, and still have plenty of mana left for reactions and removal during your opponents turns
Elven Riders Rarity: Uncommon TYPE: Creature SUBTYPE: Elf CMC: 5 Mana cost: USD: $9.25 EUR: 9.79 TIX: 0.00 EDHREC RANK: 26540 (3/3) This creature can't be blocked except by Walls and/or creatures with flying
Even the base printings of Gemstone Caverns are worth around $50, so no matter what, you'll be happy to open a copy, and very, very happy if you happen to open Gemstone Caverns #51.
Force of Negation as a three-of in the sideboard is for similar reasons, as I want to be ready to have at least a semblance of chance against decks like the Neoform deck, given that well have to deal with it for some time until it naturally bans itself out of the format
Some players loved the innovative new Infect decks in MTG 's Modern and Legacy formats, while other players disliked it for enabling fast and relatively non-interactive games