in the accessories of som weapons and some paintings and camos, there is "requires regeneration" to unlock what is that and how to get it?
If it is the same as the first game Derrame, you will have to get to Level 50, then you will be given the option if you want to "Regenerate" or not. If you do, you would now become a Generation 2 pilot, but your level would go back to Level 1. In the first one this also made you lose all weapons and upgrades you had unlocked, so you would have to unlock all of that again as you worked your way up through the levels. In the first one, the only real reason to do this was to have more available Burn Card capacity. Other than that, it was just to say you did it or because you wanted new generation challenges to have to complete. I think I saw in another thread that there are no generation challenges in Titanfall 2, so other than to unlock the items you are talking about I don't know if there are any other benefits to regenerating.
You have to technically get to Level 51. I'm currently Generation 2 on PS4. You basically start all over at Level 1 and have to unlock everything again. However, you get to keep any weapon attachments you had unlocked as well as anything you bought with merits. As far as weapons regenerating though, they do that automatically at Level 20. There are no generation challenges but if you want certain camos, banners, patches, etc. you'll need to Regenerate.
Yeah, I miss them too. I think the beauty of the regen challenges was that it served 2 purposes: 1) It gave you like secondary missions (like mini games) inside the game and it was very gratifying to complete them. 2) It forced you to use all of the weapons at some point (pilot and titan), which you otherwise probably never would have done. This actually served two sub purposes: a) Not only did it force you to use all the weapons, but it forced you to learn HOW to use them at least good enough to be able to complete the challenge. Going through this process in some cases might make you realize that you actually really like a weapon that you would have dismissed if you had just tried it briefly and got frustrated with it. b) The best way to learn how to defend a weapon is to learn how to use it and HOW it is used. Therefore, being forced to learn HOW to use them at least good enough to be able to complete a challenge, you've also gained insight on what is the best way to defend each weapon.