They've added five new general skills.
Some more pics of the new mutagen menu.
How it works: The big centre mutagen is called a synapse. These 12 new synapses take normal mutagens (red, green, blue) and EXP points to unlock, and research to identify. There's a specific NPC you have to go to do that, called Professor Moreau. His story is quite tragic, it was one of the things I read about that was added in the 1.12 strings.
Anyway, this new system apparently allows for easier mix and match (or hybrid) builds. With this new system, the four new skill slots can change colour, as you upgrade the centre synapse. So you could have two red and two blue. At least, I think that's what it trying to be said.
The more mutagen skills you upgrade, the bigger the centre synapse gets - level 1,2,3 ect. Every time that synapse upgrades,
you get an extra slot (one of the four). The centre mutagen will give bonuses to the ability slots that are above or below it.
You can see all the new armours, and their stats in this video. Go to around 17m30s.
All the Grandmaster armours are level 40. No Viper Grandmaster, as that one is already level 39.