With Battlecry giving stealth, if you attack it loses the stealth, so its just a 8/8 rush
To add more of a flavor to the Fel Reaver I would like to see something like:
Overkill: Shuffle this back at your deck while keeping its stats and reducing its mana cost to 0.
Keeping the stats so its not so abusive, shuffling back into the deck so it becomes truly unpredictable. You know... making this truly sneaky.
It's flexible. You can Rush with if it you want and attack right away (surprise Fel Reaver ambush!) or you can choose to keep the Stealth and Magnetize something onto it next turn or just attack something else after playing stuff.