There is so much cool stuff coming in Steven's Summer Adventure! It is going to be super intense! The Mary Sue has some great spoilers, and as usual we put 'em below the break!
Looks like that new gem, revealed in this promo:
Is most definitely Bismuth! She's also voice by Uzo Aduba, most well known for her role in Orange is the New Black. And it appears the musical episode that was previously alluded to is airing on the 19th, so it'll be the second episode of the Steven Nuke. Check the link for more info on upcoming episodes!
The Return of Steven Universe Includes Guest Star Uzo Aduba and an Entirely Musical Episode!