Currently, it is still day 1 of the expansion and way too early to tell if there is a need for a Nerf regarding it's effect.
It is however not too early to fix the actual issue, the animation timing problem. This is a long standing problem that I don't understand how Blizzard has not addressed, but card animations should not eat away at the timer of the following turn. Animations that occur from the moment the player ends his turn should be counted in a separate phase and only after this phase concludes and the next player starts his turn should the timer begin.
The first issue that needs to be fixed is the animation being too long. The deck is great if you know what you're doing, but it's not that easy to play with, pretty much like every other otk deck out there. If a nerf is indeed needed, I think blizzard would change Grumble so it doesn't reduce the cost of minions it bounced, If that feels too bad, make it bounce all minions and change it's cost 8, or even 10.
Shudderwock is not Broken, and while there is a huge bug/issue with how long it takes to resolve the effect, the real problem is that there are no more combo disrupting card. Coldlight is gone, along with dirty rat, iceblock, deathlord has been gone awhile. The only disruptive card left is naturalize or something like hungry dragons deathrattle. If we still had dirty rat, it would be 2 of in most non aggro decks and shudderwock wouldn't stand a chance. Combo has almost always been peoples least favorite archetype to play against, som blizzard should make ways to interact with those combos. A quick fix now would be to change saronite chain gang, but in the long term blizzard needs more combo disrupter cards.
3. ITS A DECK LIKE EXODIA.. YOU MAKE THE COMBO GOOD YOU WIN BASICALLY
In my opinion it is broken because its much easyer to get the combo (if you compare it with exodia) and there is simply no way you can die with healing rain and the massive taunts. Exodia depends on freeze and ice block but this deck has board control with minions and still waits for the comb.
If it gets detroyed / returned to hand the battlecry chain should end.
Look at the post above you! The original Shudderwock never gets returned, only the copy is returned. That means, if it gets the Yogg treatment, nothing will change. The equivalent is if Yogg casts Molten Reflection on itself, then returns the copy with Shadowstep, then the combo is not interrupted, because the original is still on the board.