It happens every playoff, the first 2-3 games of the playoffs is a regular season game, for the refs, the players, and the coaches.
The refs - first 2 games they impose their will, call everything by the book to keep things in check, after that they let them play, it's playoff hockey (look at the lack of pp in round 2)
The players - after 2 games of being body checked, blocking shots, being trash talked, they have to find another gear, raise their level of awareness and try to impose their will in a game, going to the dirty areas, keeping the game simple, fighting off harder checks and a playing in the corners and in front of the net.
The coaches - after 2 games, coaches need to change their game plans as the other teams adjust and change their set plays, lines, and so on.
Marner is a talented player, he just needs to learn how to make an impact when the game changes, he needs to adapt to the tougher game, tighter checking and not be afraid to get in the scoring areas.... he's not the only one, JT, Willy and AM also need to adapt......watch ROR get to the dirty areas, it's just he isn;t as impactful as he once was.