Mustard and I did a video on Atrocitus and Grodd after E3, the atrocitus stuff is pretty similar, except for one big nerf.
He used to be able to do Blood lift, MB, then hit another blood lift, then mb again. He could do this as long as he had bar for MB. It gave him crazy damage and a full combo anywhere on screen. He can only do one MB blood lift per combo now, so if you wanna loop it more than once, you'll need trait.
With trait you can regular blood lift into trait shot, which lets you b23 into blood lift, as b23 restands.
The combo used to be b23 blood lift mb, b23 blood lift MB, B3 into either jump in b23 or just raw b23 punchwalk. Did like 55% or something.
At gamescom i had to change it to b23 blood lift, trait shot, b23 blood lift MB b3 etc. You get the idea.
This is all hella basic though, didnt have time to search much. You can b23 into his blood regen though, then obviously you can MB that later to be an attack, so i dunno how that would work.
TLDR: Trait allows him to play his game, and it makes everything safe and extends combos. It's like sinestros old shot but he hasnt got a limit, its just a meter that takes longer to go down than sinestros shots did to disappear. You pretty much have to hold everything until his trait runs out. I guess you could push block, but i dont remember push block making it vanish. He used to get big damage off looping blood lift, but he cant do that anymore.
B23 is a great string and b2 is a sick mid. He has other strings as well, but b23 is the one you're likely going to use the most, especially with trait.