There are plenty of quality cards that synergize well with Herald of Secret Streams, and you dont have to work hard to have creatures with +1/+1 counters in this format
A big part of what keeps this fair is that Mana Leak is missing a lot of things by the point in the game Mystic Confluence is getting cast
For example, during a Bloomburrow Limited event, you can't add Relentless Rats from your personal collection
Stormchaser's Talent is one such Class: If it exits and then returns to play, you'll get a second 1/1 blue Otter token, and if it gained a level before being exiled it will be reset, and you'll be able to use the second ability to fetch an instant or sorcery from your graveyard a second time
Synonymous with control strategies, the blue and white color pairing of Azorius has long been a staple of nearly every format of Magic: The Gathering
Newer titles have moved away from the paradigm of the heroes of light collecting the scattered crystals in favor of broader, more convoluted plot-lines, but most games in the series still have a crystalline element somewhere
