The 5E PHB and DMG don't say much about the process of gaining a level and the associated new class abilities. See PHB p.11-12.
Do you apply any rules from earlier editions? Do you apply any non-rule traditions? What has happened, at your table, when PCs gain levels?
Is this accurate RAW:
Bruenor, Travok and Kairon defeat the two goblin sentries at the antechamber. Combat ends. Immediately as combat ends, the GM assigns XP. Travok gains his third level of Paladin, rolls a new hit die, and chooses the Oath of Devotion. He had already used 10 HP worth of Lay on Hands, but now that his pool jumps to a total of 15, he then uses those remaining 5 points to Lay On Hands again. He gains additional spell slots. He would require a Long Rest to change his list of prepared spells, but Oath of Devotion paladins always have Sanctuary and Protection from Evil/Good prepared, so he can immediately cast those two spells, as of the moment that the second goblin drops to the ground.
Bruenor, who had two levels of Fighter, decides to multiclass as Druid. He instantly learns Druidic, so he pulls out that scrap of bark with the druidic inscription, and reads it. He's wearing a +1 studded leather armor; the studs are iron, and druids do not wear metal armor. Is he simply limited as if he were wearing armor without proficiency, or is he unable to read the Druidic reading on the bark until he doffs the armor? What if he doesn't take off the armor, but he just removes the metal studs?
Kairon gains her third level of Bard, rolls a new hit die, chooses the College of Lore, suddenly gains proficiency in Arcana, History and Religion, and takes Expertise in History and Medicine.
Kairon's player to DM: Hey, with my new proficiency and expertise, I reconsider what the goblin said about "No more snake coin people found.” Now do I know what that means?
Before Kairon entered the cave, she overheard a goblin say "No more snake coin people found", and an INT (History) check of 12 established that she had no idea what that meant. Now with proficiency, doubled for expertise, she'd have a good shot at recognizing the reference. Do you, as DM, allow a reroll of the INT (History) check?
Do you apply any rules from earlier editions? Do you apply any non-rule traditions? What has happened, at your table, when PCs gain levels?
Is this accurate RAW:
Bruenor, Travok and Kairon defeat the two goblin sentries at the antechamber. Combat ends. Immediately as combat ends, the GM assigns XP. Travok gains his third level of Paladin, rolls a new hit die, and chooses the Oath of Devotion. He had already used 10 HP worth of Lay on Hands, but now that his pool jumps to a total of 15, he then uses those remaining 5 points to Lay On Hands again. He gains additional spell slots. He would require a Long Rest to change his list of prepared spells, but Oath of Devotion paladins always have Sanctuary and Protection from Evil/Good prepared, so he can immediately cast those two spells, as of the moment that the second goblin drops to the ground.
Bruenor, who had two levels of Fighter, decides to multiclass as Druid. He instantly learns Druidic, so he pulls out that scrap of bark with the druidic inscription, and reads it. He's wearing a +1 studded leather armor; the studs are iron, and druids do not wear metal armor. Is he simply limited as if he were wearing armor without proficiency, or is he unable to read the Druidic reading on the bark until he doffs the armor? What if he doesn't take off the armor, but he just removes the metal studs?
Kairon gains her third level of Bard, rolls a new hit die, chooses the College of Lore, suddenly gains proficiency in Arcana, History and Religion, and takes Expertise in History and Medicine.
Kairon's player to DM: Hey, with my new proficiency and expertise, I reconsider what the goblin said about "No more snake coin people found.” Now do I know what that means?
Before Kairon entered the cave, she overheard a goblin say "No more snake coin people found", and an INT (History) check of 12 established that she had no idea what that meant. Now with proficiency, doubled for expertise, she'd have a good shot at recognizing the reference. Do you, as DM, allow a reroll of the INT (History) check?