darkSpyro

I've pretty much just confirmed this myself but I haven't yet figured out how much it adds.
It appears to add 2 points to speed which is me comparing a Series 2 Stealth Elf that had all Heroic challenges complete and an elite Stealth Elf that had the 3 annoying HC complete, the Series 2 Stealth Elf had the higher speed stats.
I compared a Legendary Chill with all Heroic's with a Legendary Chill that had the three annoying ones complete but isn't upgraded. So while a fully upgraded has stat differences between a non-upgraded Chill obviously it still appears that Elemental Power, Armor, Speed and Crit are all altered on heroic challenges. But I haven't had two that are exact same one with all complete and one with none to confirm other then my series 2 Stealth Elf has a higher speed and EP then the Elite.

Elite Stealth Elf 3 HC
Speed 51
Elemental Power 61

Series 2 Stealth Elf Max HC
Speed 53
Elemental Power 66


Fully Upgraded Legendary Chill Max HC
Speed 46
Armor 69
Crit 4
Elemental Power 59

Non-Upgraded Legendary Chill 3 HC
Speed 43
Armor 25
Crit 2
Elemtnal Power 53

to note I haven't added all my Skylanders yet so the elemental Power might differ even more when I add them all but that's as they are current as i'm adding my skylanders.

Interesting find...