Some WC3 chars

[Mecha]

Miss Jenna Proudmoore
Alliance
ally - human mage
cost: 8
ATK: 7 arcane
HP: 6
text: When you play "Miss Jenna Proudmoore" put 1 "Water Elemental" token with 4 arcane attack and 4 life to your side.
Miss Proudmoore led human survivors of Lorderon to Kalimdor were she made alliance with Horde and Night Elves to defeat Burning Legion.

Fallen Prince Arthas
Horde
ally - undead paladin
cost: 10
ATK: 9 melee
HP: 10
text: Untargetable, Evasive
Prince Arthas fell during previous war to influence of the Lich King becouse of his runeblade Frostmourne. He destroyed his kingdom and people.

Furion Stormrage
Alliance
ally - night elf druid
cost: 8
ATK: 6 nature
HP: 7
text: When you play "Furion Stormrage", you may pay 6. If you do, put 2 "Saproling" tokens with 2 nature attack and 2 life to your side.
Legend of Mount Hyjal tells that it was Furion Stormrage that summoned wisps to attack Lord Archemon and stopped assault on World Tree.

[Kueson01]

Here comes the nerd in me, Arthas was never undead, and never fell in combat, ext. He simply sought after Frostmourne to obtain its power, not knowing hte blade would basucalyl curse him, and warp his thinking.

[EBWonder]

Arthas would not be horde, but rather neutral. And as the poster above states, not undead (but rather unliving).

[MilleniumKing01]

Cool Cards