Well, anything is better with black, but Grolnok is an incredibly strong commander. I really think you need to get away from the speed, and lean more into the velocity. A couple of add suggestions would be
Millikin and
Deranged Assistant, these are great in grolnok because essentially its a mana dork that draws a card, assuming grolnok is out, and they still keep you on curve for your turn 3 commander drop. But it looks like your'e aiming to do things much faster than that. Still,
Millikin and
Deranged Assistant would probably outperform
Utopia Sprawl and
Elvish Spirit Guide in this list.
Which brings me to my next point, is this a CEDH list? You can't really drop to mid-range while keeping your Thoracle wincon, and I think this deck has PL 8 written all over it.