Card says spot a character, can I spot an opponents character with 6 damage on them and resolve one of there dice on to that character, example mace has 8 damage and has a dice showing 2 melee, could I resolve that dice on him and kill him as the card reads increase the value by 2

No. When cards refer to "spot a character" they mean your character. You can't spot an opponent's character.

Hey I wasn't the only one that had little sleep and then read that card and went WTF. Yeah, spot is only your own characters. Don't worry, you'll have plenty of characters with 6 damage on them, so it is still good card though probably not an auto include.