Hola, repuesto a ti en ingles, porque la gente quiere entender que hablamos (y solo hablo poco español)
(Hello, I answer in English, because the other people want to understand what we discuss, too (additionally I only speak few words Spanish).
It depends what style of 4-2-1-2-1 it is. Does he play 4-2-1-2W-1 (DL-DC-DC-DR-DMC-DMC-MC-AML-AMR-ST) or 4-2N-1-2N-1 (DL-DC-DC-DR-DMC-DMC-MC-AMC-AMC-ST)?
Against 4-2N-1-2W-1 there is a counter on the first page: 5-2MC-2(AML/AMR)-1. (looks quite defensive, but it contains offensive wing players (use force passing down both wings) and that is important when facing such a system.
For 4-2N-1-2N-1 there is no counter given, but it is a very centered based tactic. Use the wing offensively to your advantage. Because of his AMCs I would give 3-5V-1 or 4-5V-1 a try.
4-1-2-3, first page 4-1-4-1. (please use the well made table of positions on first page)