Discussion Youtube copyright claim

That's for the ad revenue, isn't it?
If it's just for the copyright claim and they want the video gone, it doesn't matter how many of them, unless the majority of them want revenue instead of it gone

 

You're getting copyright strikes because you're using copyrighted content without paying the royalties to use it. Moreover, I doubt you got permission from all the copyright holders of all the copyrighted material you use.

Some people may say that if your work is "transformative" enough, then your work will qualify for fair use, but that's not true. I'm going on US Copyright law, so I'm not sure if it's the same everywhere, but YouTube is owned by Google, which is an American company.
Fair use is based on four guidelines:

1. what sort of work the derivative work is and for what reason the derivative work was made (this is where "transformative use" may apply)
2. what sort of the work the copyright protected work is (this factor is far less in your favor bc the original works were creative works)
3. how much of the copyright protected work was used
4. how the derivative work may affect the market for the copyright protected work (i.e. could your work be considered a market replacement for the original work?)

You don't get off scot free because you meet only one of the guidelines, and whether your work is actually fair use or not isn't decided until it actually goes to court. Moreover, most AMVs do not actually do anything transformative with the original content since the video is nearly, if not exactly, the same as the original. My personal opinion would be that it does not qualify for fair use.

YouTube has (or had, not sure if anything changed with EU copyright and YouTube) a system (Content ID) which allowed for users to cover songs that were in a list for which YouTube made a deal with the copyright holders. The copyright holders would be able to control the monetization of the video and receive money from that monetization.

In your case, for your video to be legal, you'd need licenses for each of the clips you used in addition for the music. You're making what's called a "derivative work," and the copyright holder has the exclusive right to make derivative works of their original works in addition to granting others that right.
I'm not too familiar with the copyright of the video, but for the music, you would need to obtain a synchronization license, which allows you to put the song with a video. If you're doing a song mashup, I think you would need to get a sample license, but I'm not sure if a sample license covers everything

Note that I'm not a lawyer (nor do I study law), and this should not be considered as professional legal advice.

tl;dr AMVs are illegal (and in violation of copyright) if you're not getting the licenses you're supposed to get

 

I had a phase where I made nightcore and AMVs

I just included these in the description:
~I do not have ownership over the anime or song. All goes to the respective owners. This video is purely fan-made, and will not be used for profit or illegal sharing! I just upload music and edited clips like this to hopefully give people joy for a few minutes. Thanks!
Fair Use :
Copyright Disclaimer Under Section 107 of the Copyright Act 1976, allowance is made for "fair use"for purposes such as criticism, comment, news reporting, teaching, scholarship, and research. Fair use is a use permitted by copyright statute that might otherwise be infringing. Non-profit, educational or personal use tips the balance in favor of fair use ♥
I'd also include the name of the song and artist and everything else and linked them, but that tends to be more of a common courtesy for the people watching your video if they're curious.

The artist/company owning the song will claim the video and they receive the ad revenue from it, and may occasionally block the video in certain countries (though that doesn't happen too often) but the video will be perfectly fine. I've always used this method and never received a copyright strike, even on videos with hundreds of thousands of views. The company/artist is receiving extra revenue so they have no reason to bother you, you just need to make it clear.
If you're using a super popular song, you might want to slightly nightcore it or use a remix but you should be good most of the time.

Hope this helped!