Theros

[Farandar]

So it begins

Destructive Revelry 
Instant    Uncommon
Destroy target artifact or enchantment. Destructive Revelry does 2 damage to that permanent's controller.
"Stoke a fire hot enough and you'll never run out of things to burn."
—Xenagos, the Reveler
Illus. Kev Walker   

Disenchanting shock ? YES PLEASE
I hope this won't be THE big thing of this set, but it's nice.

[Farandar]

Name: Celestial Archon
Cost: 3WW
Type: Enchantment Creature — Archon
Pow/Tgh: 4/4
Rules Text: Bestow {W}{W} (If you cast this card for its bestow cost, it's an Aura spell with enchant creature. It becomes a creature again if it's not attached to a creature.)
Flying, first strike
Enchanted creature gets +4/+4 and has flying and first strike.
Illus. Matt Stewart
Rarity: Rare
Set Number: #3/249

Really interesting mechanic : you'd rather play the Archon for its ACC (which makes it free in many stacks) and thus boosting a creature and keep an option when said creature dies. Like it.

[Farandar]

Name: Thassa, God of the Sea
Cost: 2u
Type: Legendary Enchantment Creature — God
Pow/Tgh: 5/5
Rules Text: Indestructible
As long as your devotion to blue is less than five, Thassa isn’t a creature. (Each in the mana costs of permanents you control adds to your devotion to blue.)
At the beginning of your upkeep, scry 1.
: Target creature you control can't be blocked this turn.
Rarity: Mythic Rare

This guy is going to cost a bunch : a indestructible scry 1 for 3 that turns into a 5/5 indestructible...
In T4, it also gives full evasion to all your staff. Really not bad !

[Lysyc12]

Here's a few more I really like:

Shipbreaker Kraken   
Creature — Kraken    
6{U}{U}: Monstrosity 4.
When Shipbreaker Kraken becomes monstrous, tap up to four target creatures. Those creatures don't untap during their controllers' untap steps for as long as you control Shipbreaker Kraken.
6/6

A 10/10 that clears out blockers and demands an answer.  If you tap down something scary, like a Blightsteel, you might even get opponents to help protect it!

Voyage's End     
Instant    
Return target creature to its owner's hand. Scry 1.

A nice utility spell with loads of tempo.  Not really sure if this can make it in my stack, but I like to try and find spots for solid role players like this.  Great for beginner stacks!

Medomai the Ageless   
Legendary Creature — Sphinx
Flying
Whenever Medomai the Ageless deals combat damage to a player, take an extra turn after this one.
Medomai can't attack during extra turns.
4/3

Powerful effect, but I've found that creatures like this really require a lot of protection as they usually die before the connect.  That ability though...

Underworld Cerberus   
Creature — Hound
Underworld Cerberus can't be blocked except by three or more creatures.
Cards in graveyards can't be the targets of spells or abilities.
When Underworld Cerberus dies, exile it and each player returns all creature cards from his or her graveyard to his or her hand.
6/6

Very cool card!  Not really sure about whether he makes the cut or not, but the abilities all look so interesting the I want to at least give him a shot.

Curse of the Swine       
Sorcery    
Exile X target creatures. For each creature exiled this way, its controller puts a 2/2 green Boar creature token onto the battlefield.

Very funny card!  Come on, man, they all turn into pigs!  Plus, it's a multi-targeted removal spell, in a color almost nothing's got protection from, and it exiles!  Shame about the sorcery speed though.

[Farandar]

Good new ones

A small body, but a very annoying one :

Name: Fleecemane Lion
Cost: GW
Type: Creature — Cat
Pow/Tgh: 3/3
Rules Text: {G}{W}: Monstrosity 1. (If this creature isn't monstrous, put a +1/+1 counter on it and it becomes monstrous.)
As long as Fleecemane Lion is monstrous, it has hexproof and indestructible.
Illus. Slawomir Maniak
Rarity: Rare
Set Number: #193/249

4/4 hexproof and indestructible. Not that bad. A bit small, yet.

Name: ~Reaper of the Wild
Cost: 2BG
Type: Creature — Gorgon
Pow/Tgh: 4/5
Rules Text: Whenever another creature dies, scry 1. (Look at the top card of your library. You may put that card on the bottom of your library.)
: Reaper of the Wild gains deathtouch until end of turn.
{G}: Reaper of the Wild gains hexproof until end of turn.
Illus. Karl Kopinski
Rarity: Rare
Set Number: #201/249

This one is better. A 4/5, with deathtouch and Hexproof. Not bad. The "I Scry when you die" is a nice bonus. If you need deck manipulators...

Name: Erebos, God of the Dead
Cost: 3B
Type: Legendary Enchantment Creature — God
Pow/Tgh: 5/7
Rules Text: Indestructible
As long as your devotion to black is less than five, Erebos isn't a creature. (Each in the mana costs of permanents you control counts towards your devotion to black.)
Your opponents can't gain life.
, Pay 2 life: Draw a card.
Illus. Peter Mohrbacher
Rarity: Mythic Rare
Set Number: #85/249

A Necropotence that can turn into a beater ? Not bad.

Name: Prophet of Kruphix
Cost: 3GU
Type: Creature — Human Wizard
Pow/Tgh: 2/3
Rules Text: Untap all creatures and lands you control during each other player's untap step.
You may cast creature cards as though they had flash.
Flavor Text: "Time is fluid as a dance, and truth as fleeting."
Illus. Winona Nelson
Rarity: Rare
Set Number: #199/249

A 2/3, this guy is an utility one. Untap all your creatures and lands, AND give creatures cards Flash ? YES PLEASE !

[Wagner]

I think Erebos is bad. You'll never get it to turn in a creature, I can't remember a single instance where I had 4 black mana symbols in play. Opponents not gaining life is ok, nothing big, for the rest it's just another Greed.

Reaper of the wild on the other hand. Creatures die all the time, you get free scrying about every turn. Not a bomb, but very decent utility on an ok body.

Fleecemane Lion is barely any better than Konda, Lord of Eiganjo who is unplayable. I'd take vigilance and bushido 5 over hexproof on an already indestructible creature.

[A.-1.]

My favorite card in Theros thus far.

[Farandar]

Name: Hythonia the Cruel
Cost: 4BB
Type: Legendary Creature — Gorgon
Pow/Tgh: 4/6
Rules Text: Deathtouch
{B}: Monstrosity 3. (If this creature isn't monstrous, put three +1/+1 counters on it and it becomes monstrous.)
When Hythonia the Cruel becomes monstrous, destroy all non-Gorgon creatures.
Illus. Chris Rahn
Rarity: Mythic Rare
Set Number: #91/249

Nice but not huge, a 7/9 deathtouch that will destroy all creatures.

Name: Hero's Downfall
Cost: 1BB
Type: Instant
Rules Text: Destroy target creature or planeswalker.
Flavor Text: Destiny exalts a chosen few, but even heroes break.
Illus. Ryan Pancoast
Rarity: Rare
Set Number: #90/249

Nice removal, instant speed.

[Farandar]

Name: Dissolve
Cost: 1UU
Type: Instant
Rules Text: Counter target spell. Scry 1. (Look at the top card of your library. You may put that card on the bottom of your library.)
Flavor Text: "You thought only the gods could stop you?"
Illus. Wesley Burt
Rarity: Uncommon
Set Number: #47/249

Nice upgrade for your vanilla counterspell.

[Wagner]

Whip of Erebos
   2bb
Legendary Enchantment Artifact    Rare
Creatures you control have lifelink.
2{B}{B}, : Return target creature card from your graveyard to the battlefield. It gains haste. Exile it at the beginning of the next end step. If it would leave the battlefield, exile it instead of putting it anywhere else. Activate this ability only any time you could cast a sorcery.

I like this one, it's a Shallow Grave every turn, and all your creatures having lifelink is nothing to scoff at either.

[vaughnbros]

My favorite card in Theros thus far.

This is great!  When people want to sit there with a hand of 20 cards you can just blow them out and then smash another person for 7.

[Wagner]

My favorite card in Theros thus far.

This is great!  When people want to sit there with a hand of 20 cards you can just blow them out and then smash another person for 7.

Errr, there is a maximum hand size in most Type 4 games (usually 5 cards). Even if a player manages to have 20 cards, you'd think one of those is a counterspell or other effect to not die to this.

Still, a damn fine card, not a must counter, but it will annoy everyone quite a bit.

[A.-1.]

Whip of Erebros seems strong enough for inclusion. It's a shame that it gets hit by artifact and enchantment removal.

We play with some crazy rules (no max hand size being one). Storm Seeker and Gaze of Adamaro are really strong, so I expect the dragon to be decent as a sorcery-speed version.

[Wagner]

Colossus of Akros
   8
Artifact Creature — Golem    Rare
Defender, indestructible
10: Monstrosity 10. (If this creature isn't monstrous, put ten +1/+1 counters on it and it becomes monstrous.)
As long as Colossus of Akros is monstrous, it has trample and can attack as though it didn't have defender.
Illus. Zack Stella #214/249   10/10

Why didn't anyone post this yet? It's a 20/20 guy with indestructible and trample!