Unknown Minion.?

Hi, I am relatively new to Heroic but am loving the game. I seem to come across a minion and i am unsure as to what it is, please can someone assist me.
It seems to be a slow but powerful minion that does high melee damage. It is blue in colour and looks a bit like a big slime monster.
Please advise. Thanks.

Thats probably the Mana Wraith, its a legendary with high dmg and hp, costs 5 mana and increases the cost of the owners cards by 2 for each on the field. The best way to kill him is with swarm units like skeletons and rolling rocks. Good luck.

Thanks - do you think that it is a good unit to use? Dont like the fact that it increases the cost of my other units but i must admit i always struggle when i come up against it.

Its one of the worst legendaries, its only usefull on lower arenas, just keep him alive as much as you can, it will really hurt the enemy with that extra manacost. The best counter is pixie, keep him alive but sleeping.

OK thanks, dont have him yet but wont upgrade him if i do get it.