If you are hidden from all your opponents before the first round of combat you will surprise them and get a free round to attack them before they can react. (You are no longer hidden after you attack.) On all targeted attacks against you, the attacker must first identify where he thinks...
Paladin and some other classes is able to prepare these spells | Dungeons and Dragons 5e - D&D toos, Spells, Spell cards, Spellbooks'
Bard and some other classes is able to prepare these spells | Dungeons and Dragons 5e - D&D toos, Spells, Spell cards, Spellbooks'