"The troll dies only if it starts their turn with 0 hit points and doesn't regenerate."
Now this is two questions in one:
1. When a troll reaches 0hp, but hasn't been dealt fire or acid damage during the combat, are they still conscious, are they conscious but knocked prone or are they knocked unconscious?
2. If the answer to the above question is, 'They are knocked unconscious', do they regain consciousness once their next turn comes around and they regain 10hp from regeneration?
They are knocked unconscious when they reach 0 HP. Then on their next turn, if they haven't been hurt by fire or acid, they regain 10 HP and are conscious again.
The rules for characters and monsters are the same, but in many cases the DM will skip death saves for monsters to save time, unless it is an important enemy or NPC. For Trolls, they ignore death saves because of their Regeneration ability.
"The troll dies only if it starts their turn with 0 hit points and doesn't regenerate."
Now this is two questions in one:
1. When a troll reaches 0hp, but hasn't been dealt fire or acid damage during the combat, are they still conscious, are they conscious but knocked prone or are they knocked unconscious?
2. If the answer to the above question is, 'They are knocked unconscious', do they regain consciousness once their next turn comes around and they regain 10hp from regeneration?
They are knocked unconscious when they reach 0 HP. Then on their next turn, if they haven't been hurt by fire or acid, they regain 10 HP and are conscious again.
The rules for characters and monsters are the same, but in many cases the DM will skip death saves for monsters to save time, unless it is an important enemy or NPC. For Trolls, they ignore death saves because of their Regeneration ability.
So if a time lord is dying by isn't killed outright, they can ... oh wait, wrong nerd forum... ;P