Turn 1: Forest, Arbor Elf
Turn 2: Mountain, Flinthoof Boar, activate haste, attack for 3 (17)
Turn 3: Mountain, attack for 3, Goblin Battle Jester (14)
Turn 4: Mountain, cast Flames of the Firebrand to dome for 3, falter his only blocker, attack with Boar and Goblin for 5, cast Titanic Growth before damage for 4 more damage (2)
Pass the turn, show him Volcanic Geyser, accept the concede.