Quickleaf
Legend
15th level?
Assuming a direct confrontation without other hijinx, it becomes a Breath Weapon Damage vs. Character HP question. Assuming by "Great Wyrm CR 24" you mean an Ancient Red Dragon (which is CR 24), it's breath weapon deals 91 average damage. You don't want the dragon to be able to knock out the entire fresh party in one breath. At 15th level, a character probably has ~93 hit points on average (assuming d8 hit dice and +1 Con mod), so could withstand average damage of its breath weapon.
Or possibly 5th level if they poison a bait-sheep for dragon to eat, then ambush the poisoned dragon, knocking it prone while it's flying, ideally falling into a trapped area, and manage to stun-lock it on the ground while peppering it at range with total cover.
Assuming a direct confrontation without other hijinx, it becomes a Breath Weapon Damage vs. Character HP question. Assuming by "Great Wyrm CR 24" you mean an Ancient Red Dragon (which is CR 24), it's breath weapon deals 91 average damage. You don't want the dragon to be able to knock out the entire fresh party in one breath. At 15th level, a character probably has ~93 hit points on average (assuming d8 hit dice and +1 Con mod), so could withstand average damage of its breath weapon.
Or possibly 5th level if they poison a bait-sheep for dragon to eat, then ambush the poisoned dragon, knocking it prone while it's flying, ideally falling into a trapped area, and manage to stun-lock it on the ground while peppering it at range with total cover.
