Going twelve wins in the Arena. Means you managed to take a bunch of random cards and still managed to attain at least a 6:1 win/loss ratio - all the while fighting against others who had made close to the same progress as you.
Legendaries in a nutshell.
When turning a card containing a legendary while opening a pack, the inkeeper can barely contain his amazement
Playing said legendary is often accompanied by a tune and a Battle Cry befitting of their legendary status.
"GARROSH! You are not fit to rule the Horde!" Look out, people, Cairne Bloodhoof is back and up for a rematch.
Jaraxxus, Eredar Lord of the Burning Legion floats off the board, spins around a few times to gain hero-border, and then squashes the puny warlocknote Or priest - if you managed to copy the card prior to it being used
Jaraxxus: "You face JARAXXUS! EREDAR LORD of the BURNING LEGION!!"
Ysera doesn't enter the board with any visual effects, but every time you end your turn she opens a portal to the Emerald Dream and pulls a powerful card out from it.
Ysera: "I dream and the world trembles!"
Tirion Fordring doesn't enter with a unique effect either, but his battlecry, plus the epic music and the fact that his death gives Uther the Ashbringer makes him alone a pretty good reason to play a Paladin deck. - Giving Uther the Ashbringer is accompanied by a unique visual effect, too.
Tirion Fordring: "Put your faith in The Light!"
With the patch, more have been added, like Ragnaros making a Call Back to his Molten core days of emerging from a pool of lava.
Ragnaros the Firelord: "BY FIRE BE PURGED!"
Prophet Velen emerges onto the board glowing with The Light's holy radiance
Prophet Velen:"Not all who wander are lost."
Can't forget Deathwing. He covers the entire board in flames - and when the smoke clears, he's the only thing left standing.note Aside from any minions spawned by Deathrattles. There's a reason they call him Deathwing the Destroyer
Deathwing: "I! AM POWER! INCARNAAAAAATE!!"
Bolvar enters to Wrathgate music as a golden lion roars at his opponent, screaming at the top of his lungs:
Bolvar: "Come Forth, COWARD!"
What's even more awesome? The Big Game Hunter, the one card specificaly designed to turn most legendaries (or any being with more than 7 attack points) into his bitch the moment he enters the game! Hell, even his color text says that he got tired of hunting Devilsaurs and now wants to kill Onyxia with nothing but a rusty hunting knife!
This can not be understated. Your opponent has just played one of the biggest creatures the game has to offer, likely using up his entire pool of mana in the process, then along comes a dwarf with his shotgun. Suddenly, it doesn't matter what minion it is - if it is above 7 attack, it's dead in a single shot, no questions asked. And you still have mana left over!
Beating Heroic Curse of Naxxramas - each Heroic boss is, for all intents and purposes, the card-game equivalent of an SNK Boss with overpowered abilities and cards:
Anub'Rekhan summons a 4/4 nerubian each turn right from the get-go - and if you try to swarm him he has a Locust Swarm that deals damage to your entire board AND heals him.
Grand Widow Faerlina rains fire upon you for one mana each turn - one point worth of random damage for each card in your hand, and it's for half the mana of a regular hero power. She also has a 2/4 minion which grants her a three-damage attack, and the effect of these STACKS.
Maexxna pretty much makes playing non charge/non battlecry minions worthless by webbing two creatures back to your hand each turn - oh and it's free. She also starts with two Haunted Creepers already on the board
Noth the Plaguebringer gets a 5/5 skeleton whenever one of your minions die - also has the card Plague, which destroys all non-skeletons
Heigan the Unclean gets a Free Hero power that deals 3 damage to your left most minion, meaning he gets a few turns to build up his side of the board unless you use spells, and he starts with a voidcaller already on the board
Loatheb Has 99 HP and a free hero power which deals 3 damage to your hero, he also starts with a Fen Creeper a 3/6 with taunt and a spore on the board
Instructor Razuvious has a one mana hero power that deals 4 damage and his Massive Runeblade deals 10 damage to minions and 20 damage to your hero
Gothik the Harvester has a hero power that draws him a card and gives him one mana crystal and when Certain minions of his die You get a 0 attack ghost that deals one damage to you a turn
The Four Horsemen Have 3 2/7 minions that make Rivendare immune already on the field, Unless you draw the right cards early you won't be able to do much before they win
Patchwerk only has a 4/8 hook with Windfury and his 4 mana hero power which destroys a minion and that is all he needs
Grobbulus gets a free hero power which deals 2 damage to everything on your side of the board, He also has his Mutating injection which gives +4/+4 and taunt which he loves to give to his echoing oozes
Gluth constantly reduces your minions Health to 1 with his hero power and his Jaws can get very powerful very quickly with all his deathrattle minions
Thaddius will have both Fuegen and Stalagg come onto the field on his first turn
Sapphiron kills all your minions for free at the start of his turn because the Frozen Champion does not appear
Kel'Thuzad starts with 20 armor and 45 health and his hero powers deals 3 damage and freezes your hero in phase 1 and a 8 mana mind control a random minion in phase 2
One for Kel'Thuzad, Despite being Lighter and Softer than his normal incarnation, he's still Dangerously Genre Savvy; doing certain actions while playing heroic Naxxramas will cause him to get upset and nullify the action without refunding the cost.
Upon using Alexstraza against Heroic Loatheb, who has 99 hp, he will snidely remark: