Some mild flirting.

A few female characters wear midriff baring outfits.

A couple instances of male characters not wearing shirts (in a non-sexual manner).

Rogue kisses Gambit once.

Characters get punched, thrown across rooms, scratched and bruised, almost caught in explosions, objects thrown at them, and knocked out. No blood or gore is shown and the violence is not graphic.

In Season 4, Apocalypse plans to turn everyone into mutants; it's mentioned that most of them won't survive it.

Characters have near death experiences throughout the series, though they are non-graphic.

Some mild insults.

"What the devil" is used twice.

None

Plenty of suspense, especially in later episodes. Some of the fights can get intense.

Blob kidnaps Jean in one episode; though nothing happens, it can be somewhat unsettling.

Hank McCoy's transformation into his blue, hairy form might scare some younger children.

Two potentially frightening characters are Legion and Apocalypse.