Transfer Student is the newest card to join Hearthstone and is currently available for free simply for logging in!
The card effect states that based on the game board you're playing on, you're going to get a new effect. We've gone through each of the boards to figure out which effect each one gives Transfer Student. The effect is usually based on mechanics that arrived with each game board's associated set, or it has an effect based on the board's flavor.
Transfer Student's Card Effects by Gameboard
Here are all the Transfer Student effects that are currently available in the client. Since the board for Scholomance is not yet available, much like the dual-class cards, that effect won't be seen yet.
- Orgrimmar - Battlecry: Deal 2 Damage
- Stormwind - Divine Shield
- Stranglethorn - Stealth, Poisonous
- Pandaria - Battlecry: Give a friendly minion +1/+2.
Expansions (Pre Years)
- Naxxramas - Deathrattle: Add a random Deathrattle minion to your hand.
- Goblins vs Gnomes - Battlecry and Deathrattle: Add a Spare Part to your hand.
- Blackrock Mountain - At the end of your turn, reduce the cost of a random card in your hand by (2).
- The Grand Tournament - Inspire: Draw a card.
- The Museum (Explorers) - Battlecry: Discover a new Basic Hero Power.
- Excavation Site (Explorers) - Battlecry: Add a random weapon to your hand.
Year of the Kraken
- Stormwind (Old Gods) - Battlecry: Spend all your mana, summon a minion of that cost.
- Karazhan - Battlecry: Add a Karazhan portal spell to your hand.
- Mean Streets of Gadgetzan - Battlecry: Give a random minion in your hand +2/+2.
Year of the Mammoth
- Un'goro - Battlecry: Adapt.
- Frozen Throne - Deathrattle: Add a random Death Knight card to your hand.
- Kobolds and Catacombs - Battlecry: Recruit a minion that costs (2) or less.
Year of the Raven
- The Witchwood - Echo, Rush.
- Boomsday - Taunt, Battlecry: If you have 10 mana crystals gain +5/+5.
- Rastakhans Rumble - Rush, Overkill: Draw a card.
Year of the Dragon
- Dalaran - Battlecry: Add a Lackey to your hand.
- Uldum - Reborn.
- Uldum (Alt) - Battlecry: Add an Uldum plague spell to your hand.
- Dragons - Battlecry: Discover a Dragon.
Year of the Phoenix
- Ashes of Outland - Dormant for 2 turns, then deal 3 damage to two random enemy minions.
- Scholomance Academy - Battlecry: Add a Dual Class card to your hand.
The Effect Will Update for a Couple of Years
Hearthstone's Chadd Nervig has confirmed that the effect will be updated as new expansions come out, though once Transfer Student moves out of Standard, those updates will cease.
This is basically correct. We plan to update Transfer Student with custom effects for new boards, while he is in Standard. After he rotates to Wild, new boards will get a consistent "Battlecry: Discover a <Expansion> card." for each board.
Plans may change in the future, but that's what we're thinking right now, at least.