When he's on his game, he's phenomenal and easily one of the best players in hockey offensively and defensively. When he's not, he's worse than useless. He creates nothing, cowers away from contact, and becomes extremely error prone. Every player has good games and bad games, but most stars find some ways to contribute in positive ways when they're not scoring. Marner simply doesn't have that ability. He also has an extremely frustrating personality and loves to say the wrong thing
Issue is, he's never once been on his game in the playoffs.