Hearthpwn

Wait,WOT? it is not Power Overwhelming? wtffff

Corruption

EDIT: damn, 2 seconds too late, I guess I will go with Shadow Bolt

Blood Imp

Demonfire/Demonheart?

Sacrificial Pact

Quote from FoggyFogGG >>

Quote from Shadicar >>

Sacrificial Pact

 Correct!! You're right it's Sacrificial Pact !

Two same shadows fighting in the dark.       ---- Warlock vs Warlock, obviously it's a dark class.
Possession always leaves a mark.                 ---- Jaraxxus possession leaves a mark of 15 life cap.
Alas the one to be possessed.                       ---- Alas to the Warlock possesed by Jaraxxus.
Cuz the free one will conquest.                    ---- Cuz the free Warlock can conquest with one card only.

Also the anagrammatism of the capital letters form the word PACT.

 

You're up for the next riddle.

Quote from FoggyFogGG >>

Quote from Shadicar >>

Sacrificial Pact

 Correct!! You're right it's Sacrificial Pact !

Two same shadows fighting in the dark.       ---- Warlock vs Warlock, obviously it's a dark class.
Possession always leaves a mark.                 ---- Jaraxxus possession leaves a mark of 15 life cap.
Alas the one to be possessed.                       ---- Alas to the Warlock possesed by Jaraxxus.
Cuz the free one will conquest.                    ---- Cuz the free Warlock can conquest with one card only.

Also the anagrammatism of the capital letters form the word PACT.

 

You're up for the next riddle.

When you feel the coldness creeping
Grieve yourself but not the weeping
Utter words of times long passed
Speak quickly though - they'll be your last

Maybe now Corruption? Last words, like last turn before "cold" death.

Nope and nope.

Nozdormu

Nah. However, stick with that weeping part ;)

Frost Elemental?

Try to find the meaning of the (two) last line(s) first. That should narrow it down quite a lot.

Kel'Thuzad?

Wailing ghoul or what ever it's called? The card from Nax that silences all your minons 

Wailing Soul, but since that was guessed, Doomsayer.
Coldness refers to Freeze Mage where Doomsayer's a staple.

Quote from MagicalCrocodile >>

Wailing ghoul or what ever it's called? The card from Nax that silences all your minons 

Quote from Shadicar >>

Quote from MagicalCrocodile >>

Wailing ghoul or what ever it's called? The card from Nax that silences all your minons 

Wailing Soul. That's indeed the right answer. 

When you feel the coldness creeping (soul, ghost, you get the idea)
Grieve yourself but not the weeping (you are the one affected, not the wailing soul)
Utter words of times long passed (say things about the dead ones...)
Speak quickly though - they'll be your last (...before you get silenced)

Quote from MagicalCrocodile >>

Quote from Shadicar >>

Quote from MagicalCrocodile >>Wailing ghoul or what ever it's called? The card from Nax that silences all your Iminons 

Wailing Soul. That's indeed the right answer. 

When you feel the coldness creeping (soul, ghost, you get the idea)
Grieve yourself but not the weeping (you are the one affected, not the wailing soul)
Utter words of times long passed (say things about the dead ones...)
Speak quickly though - they'll be your last (...before you get silenced)

 Cool! My turn : 

In a building of wood and straw

where certain creatures just might crawl

I give protection to those In my care

But I'm rarely seen, being more then rare. 

Not the best, but it'll do!  

Siltfin Spiritwalker?