TYM just got word from an inside source who has confirmed that there is an Injustice 2 Anniversary Multiverse up with some pretty stellar rewards. It seems like it's just a series of boss towers with no prior requirements needed to play through them.
Word of warning, the recommended level for doing these are 30, so expect things to be a challenge if you don't have a character just quite there yet. However, for completing that challenge, you can expect to get a ton of Platinum Motherboxes as well as 3 Diamond Motherboxes and 1000 Source Crystals for completing everything. You only have 163 hours (about a week) to finish this, so don't miss out!
Big thanks to @Sage Leviathan for being our secret inside man and also providing the images you see above.
Anniversary Multiverse Up with Great Rewards