So dragons can only make one opportunity attack per turn?

Constitution ability check or Constitution Saving Throw?

Lunging Attack + Sentinel, monster moves around PC in a 10ft, do attack of opportunity happens?

Slow spell, do you need to have line of sight on creatures to affect them?

Can a Monk use either Dex or STR for grappling attacks?

Lucky Feat, The second use on the enemy attacks roll, which one of these statement are true?