Only player to be in playoffs of both a major and Champions is ScreaM (major playoffs in DHW13 and Cologne15) And will probably be the only player for a long time be in the Semifinals of both. (DHW13 and Champions)
Shahzam is only player to be in playoffs of major (London 2018) and win an International Masters (Masters Reykjavik). He was also in the playoffs of Masters Berlin.
yay has been in the playoffs of major (London 2018) and was in the finals of Masters Berlin.
Hiko has been in the playoffs of one major (Cologne16, Columbus16, Cologne14, Kato14, and DHW13) and the playoffs of an International Masters (Masters Berlin)
Nitr0 has been in the playoffs of 5 majors as well (Berlin19, Kato19, FACEIT18, Cologne16, Columbus16) and the playoffs of an International Masters (Masters Berlin)
Ethan has been in the playoffs of one major (Berlin19) and the playoffs of one International Masters (Masters Berlin)
Players to reach playoffs of a major and a VCT Season 1 Masters (all regional) are:
ANGE1 (FACEIT18/DHW14,Kato14,DHW13)
Ex6TenZ (DHW13)
RUBINO (ELEAGUE17)
As well as all players listed above