A few AOE spells use the wording "...when first entering the area ... or ending it's turn there". The question is, is this "or" inclusive, (A creature that enters and remains for the duration of it's turn will take the damage twice), or exclusive (the creature will only take damage once for entering, even if it ends it's turn in the AOE)?
It seems that if the "or" is exclusive, a creature would have to spend two turns in the AOE to trigger the condition "ends it's turn there", which would be an incredibly rare situation.
Some examples:
Wall of Fire:
One side of the wall, selected by you when you cast this spell, deals 5d8 fire damage to each creature that ends its turn within 10 feet of that side or inside the wall. A creature takes the same damage when it enters the wall for the first time on a turn or ends its turn there. The other side of the wall deals no damage.
Insect Plague:
When the area appears, each creature in it must make a Constitution saving throw. A creature takes 4d10 piercing damage on a failed save, or half as much damage on a successful one. A creature must also make this saving throw when it enters the spell's area for the first time on a turn or ends its turn there.
This question is similar, but unresolved: How much damage does a creature take for spending its entire turn inside a Wall of Fire?
