Elves is a combo-oriented green deck that uses Gaea's Cradle, Priest of Titania, and Wirewood Symbiote to generate explosive mana and overwhelm you with creatures. Wrath of God and Powder Keg are your most important cards — Keg on 1 wipes most of their mana dorks and Wrath cleans up the board entirely, so protect these at nearly all costs. Standstill is awkward here since they will break it freely to develop their board, so consider being selective about when you deploy it. Phyrexian Furnace has no relevant targets against a pure green creature deck, so it comes out to make room for a second threat in Exalted Angel and an extra Powder Keg. Post-board, watch for their Naturalize effects targeting Powder Keg — hold Counterspell and Mana Leak up when you go to pop it.