How can I get Angra Mainyu?

Yes , i already have it.

Very rare but very possible. I got him at np2. Just think about all the 1-3 star CE's, servants, exp, and fou cards possible in the friend summon pool plus the low drop rate... There's a lot of competition to get him to drop.

Yeah I feel like it’s even lower than the rate of getting a 5 star from quartz summon. I spent like 200k for my first one then managed to randomly get him from free daily.

It is incredibly rare, I’m extremely lucky as is having him at Np 3 when most people don’t even have him even after 1 mil+ fp.

It is possible, but not something to stress yourself with. The rates for summoning him are extremely low (about 0.02%, much lower than the odds of pulling a 5* servant). I spent over 200k FP to try and get him, to no avail. But when I rolled for event CEs, he spooked me twice. Keep rolling, he'll show up eventually. In the meantime, feel free to use mine if you want. I actually grailed him since he looks great as a trophy. Sadly, not that great as a servant though.

I got him while trying to np5 Euryale. Spent ~0.5million FP and got him but 0 Euryale. His stats and skills were so bad that I didn't bother to raise him. So no need to stress if you don't get him.

I've rolled uncountable levels of FP. Still nothing. That is the nature of gacha.