Ya I knw dis trap bt on King's side seen 4d first time
My 8-move mate.

I think best for black is
6...dxNe5 then if
7QxBg4 Nxc2+ etc.
I believe Legalls mate only works if black has developed neither knight. A generality perhaps, but like most generalities, generally true.

Rainbow,
I sympathize with your board posting problems, and have had my own frustrations.
Instead of 8...Nxa1, in your blue line, 8...Ne3+ screams. Even 8...Nf6 (rather than 7...Nf6) picks up a tempo and development and then the rook (really just the exchange).
I think my main point holds. That Legall's mate only works if black's knights are undeveloped. Lots of variations though, and it remains a good pattern to know. I have only used it once OTB, in 52 years of play.
An unexpected kings gambit variation lead to an 8-move checkmate.