Singleton break on a chosen card, so you can play 4fourBiovisionarys or four Hedron Alignments
He's a phenomenal sacrifice outlet, has discard synergy, proliferates on demand, distributes -1/-1 counters and therefore acts as removal, and even has protection from Humans as a built-in safety valve from the most popular creature type in Magic.
I did a bit of research, and I believe that right now, the top two decks in Standard (GB Delirium and UW Flash) are about as dominant as they have been over the past few years, but there isn't one deck (or card) that's dominating (or breaking) the format
Cards with amass 1 are at their best when theyre adding another body to the board, not when theyre adding a +1/+1 counter, so sacrificing armies to keep the sac fodder coming is your best bet
#5 Black Vise - Golden Age The devil guarding the gates of hell
I absolutely love this kind of collage art that combines hyper-detailed paintings with these abstract backgrounds