Magnus Carlsen

He's actually the 2nd best.

Magnus is actually unarguably the number one chess player in the world

Magnus is the 2nd best, but in Blitz, only behind Nakamura. He is the best classical player.

He just become rapid and blitz world champion so I'd say he's number 1

Yeah, and he just won the world Rapid Champion title too, so he's world champ in all 3 right now (classical, rapid, and blitz).

What if there's somebody better? In the shadows lurking

Let's be honest, I can beat him blindfolded, with one hand tied behind my back, playing with 500 ping, on a chromebook track pad, and with time odds. Easy win. 

Oh OK llama. I didn't know that

In online play, specifically blitz and bullet, there seems to be a relative parity, although Mr. Carlsen definitely has a slight, and sometimes big edge over most of his competition/contemporaries. His closest online competition (at least from the standpoint of the 2022 SCC championship match) appears to be Mr. Hikaru Nakamura, who won the match overall, but was ironically outscored in the final two time control portion, the first portion obviously being the exception. If anything, it really impressed me how Mr. Nakamura was able to win the match, and I really appreciated that from a spectator standpoint, Mr. Carlsen was never out of the way of making a comeback. If anything, I would say that for online blitz and bullet, I think Mr. Carlsen and Mr. Nakamura are close, with Carlsen having a slight edge. However, for online Rapid, OTB Rapid, Blitz, and Classical, I would argue that he seems noticeably more dominant, with Classical probably being his highest level of dominance. Granted, this year for Rapid and Blitz, he looked solid all year and exceptional at the championship though there was definitely parity with so many other players having good chances of winning!

Some guy who is on line sometimes.

I am not magnus

Magnus Carlsen is the world champion at the moment, and has the highest rating in blitz, classical, and bullet. He's without any doubt the best player living, but it's also reasonable to consider him the best who ever lived. If you take away the requirement for organic life, however, he definitely can't beat Stockfish at the highest setting, because no one can. Oddly, that means he might not be able to beat Mittens, depending on what that bot actually is.

Magnus himself has said that the true test of chess ability is blitz, not classical.  He said that before he lost to Hikaru, of course.