I have 2 questions.

1: do you have to read trinity war before forever evil?

2: is it okay to just read forever evil arkham war?

@paalern3

1. You don't really have to read it to understand Forever Evil, but I still thought it was a good story a good whodunit/mystery plot so I'd still recommend reading it, but it is not necessary for Forever Evil. If you don't feel like reading it then all you need to know from it is that (Spoilers for Trinity War if you decide not to read it) the Crime Syndicate (an evil version of the Justice League) from Earth-3 (a mirror imaged parallel Earth) has managed to break through to our Earth and has apparently managed to defeat the Justice League.

2. Sure I guess you can do that if you want, Arkham War is probably the best tie in for the event in my opinion and is basically just about what's happening in Gotham and Arkham in Batman's absence, the story focuses around Bane alot. However this event is called Forever Evil so reading the main series is where the story is at and where the big stuff is happening. I personally have enjoyed it so far and if you are a big fan of DC's villains (specifically Lex Luthor, Black Manta, Captain Cold, Bizarro, Black Adam, and Sinestro) then I think you're just going to love the story as it centers around them and how they are basically the only hope to defeat the Crime Syndicate, they are all characterized and written very well (especially Luthor in my opinion) You don't really have to read any other tie ins to understand the story so reading the 7 main issues will do just fine. Although I did like the Justice League title tie ins as they went more into depth about the Crime Syndicate and it explained their back story and stuff.

Thank you, I've heard that nightwing has a role, is this in arkham war?

@paalern3: No, his role is in the main series. All I'm going to say is that stuff goes down for Nightwing. Specifically in issues 1 and 6