The general strategy is to deny your opponent the ability to reach your sites, either by directly preventing movement or presenting large threats to overcome. In the meantime, the secondary goal is to accumulate a good amount of cards to support Battlemage, both spells and equipment. Alternatively you can use grappleshot or teleport to get an early alpha strike in while your opponent is still preparing. When sideboarding, consider strategies which are propped up by key units or overwhelming your minions. Good cuts include Grappleshot for the anti-horde options, as you will likely want to play more defensively, or Crown of the Victor/Screaming Skull for the other options, as these provide more fringe/difficult to obtain benefits within the larger strategy.

Minions:

-Alvalinne Dryads: Mostly for the extra mana, they can also sit on a Mountain Pass to block movement.

-Cerberus in Chains: A bodyguard for Battlemage, Cerberus is forced to follow but notably doesn't tap, meaning it can help attack or stay open for defense.

-Hillock Basilisk: Helps in forming the defensive line to keep your opponent away from your sites, best placed adjacent to an occupied Mountain Pass.

-Royal Bodyguard: Can tag along behind Battlemage to help mitigate any damage he takes in combat, he only needs to be nearby and his ability isn't effected by the disabling effects.

-Daperyll Vampire: Very efficiently costed for her effects, but she is paticularly good at offsetting damage Battlemage may take.

-Stone-gaze Gorgons: Similar to the Basilisks, they put pressure on a wider area though will need to be used more tactically, neither them nor the Basilisks effect Battlemage which is noteworthy.

-Panorama Manticore: An alternate threat to the Battlemage strategy, can avoid some of your own obstructions, lethal is useful on both offense and defense, and its last ability is likely to trigger in this deck, allowing it to be both offensive and available for defense in the same turn.

-Death Dealer: Generally a good card to keep in hand until necessary to clear the way to the enemy avatar or remove unanswerable threats, best used after building up a good hand of cards/effects for Battlemage after getting a good lock on the game.

Magic:

-Divine Healing: Heals Battlemage for a fair bit on the cheap, allowing him to be a bit more risky in combat.

-Teleport: Used to hand deliver Battlemage to a site, usually this will be the enemy avatar once you have a decent supporting suite to back him up.

-Critical Strike: Helps with Battlemage's damage output, can be used to one shot the enemy avatar with Gigantism and any other buff.

-Blaze: Helps Battlemage get through a dense board of enemies, and does some damage as a bonus, can also help rearrange lock pieces such as Basilisks or Gorgons, perhaps also catch another large unit up to assist in combat.

-Grapple Shot: Very useful to help push either Battlemage or Vampire up the realm and get a free strike in.

-Infiltrate: An all star, can help get extra damage in, defend Battlemage, disable a threat, or steal a static effect, the unit does not need to be immediately used and is even harder to target because of stealth, making it a possible ace in the hole for later.

-Gigantism: A very good finisher and not much else.

Artifacts:

-Philosopher's Stone: A very good piece for reducing mana costs, considering the deck is three elemental types.

-Crown of the Victor: Battlemage will most likely be killing something, so this is likely to quickly become an upside, might be hard to find a weak enough minion to kill if your opponent knows this is in play.

-Screaming Skull: Allows Battlemage to either deal with multiple, smaller enemy threats at once, or otherwise move after killing one.

-Flaming Sword: Very good for clearing multiple threats at a time, makes it much trickier for the enemy avatar to defend against his strikes as the splash damage will hit them regardless, also provides a small, but permanent buff which is useful.

Sites:

-Holy Ground: Helps heal Battlemage, best used in the midgame before he reaches the enemy avatar so only he is likely to get its benefit.

-Gnome Hollows: Can help lock out larger threats from the opponent and force them to engage your minions fairly.

-The Colour Out of Space: Generally good attunement fixing, you will likely want to play sites forward aggressively and leave a void near the rear anyways.

-Steppe: Fixing for Earth and Fire.

-Mountain Pass: Helps block the opponent from coming closer, as their minions can't pass through it or enter it to attack as long as you have something parked here, such as a Dryads.

-Dwarven Forge: Helps play some of the equipment for Battlemage quicker, as well as fixing for Fire.

-Ruins: Fixing for Air and Fire.

-Imperial Road: Can help accelerate you establishing a path for Battlemage, especially as you can punish greedy opponents who over commit their deployment by attacking the site they get, if they deploy too far away from their others.

Sideboard:

-Disintegrate: Targeted removal for if the enemy requires a certain minion/artifact.

-Poison Nova: Battlemage is likely to be in the enemy's backline, making this good for clearing out minion heavy boards.

-Cone of Flame: Also used for minion heavy strategies, with the added benefit of being able to help get some extra damage in on their avatar.

-Magellan Orb: They'll never see it coming (maybe).