Crossword puzzle clue "hardest difficulty level often"

Hardest difficulty level, often

First video game with a selectable level of difficulty

Low-level pollution or high-level protection

Warning sign at a train station's food court? (NOTE: The original sign, without my additions, actually exists. It's in Grand Central Terminal in NYC, on the lower level — the food court level. The sig

Class, level or class level

Management level or theater level

The hardest part when making guacamole?

Hardest to eat, as fish