Magnus is an exception to the rules on what openings you can play at top level, mainly because he is so good at manipulation of middle game positions compared to most, a number of years ago i went to Norway as spectator and watched Magnus topple a 2680 player with black using tge following: 1.e4,Nf6 2.e5, and then replied ...Ng8!? his opponent scratched his head for 25 minutes play continued: 3.d4,d5 4 Be3,Bf5 5.g4,Bg6 6.h4,h5 and you can see how Magnus has already Manipulated the position into a type of caro kann advance from such a strange opening, I know of no other player who can do this who can play what looks like an iffy opening but within half a dozen moves is Questionably worse!!?
Still …. They are saying B4 is not played at top level.
Sort:
https://m.youtube.com/watch?v=yFlM2-VFKCU
Magnus played this opening and was ridiculed. Commentators recommend chess players not play it
Meanwhile, Magnus plays C3
and legitimises this variation versus C4 to devotees of this excellent opening . Chess from move one. Giri shocked enough to pause.
Draws common but there is solid theory with this opening.
Something Carsten Hansen also saw and improved on.