What does "when it enters the spell’s area for the first time on a turn or starts its turn there" mean?

Question

From When do you roll the damage for Cloud of Daggers?, it was suggested that some comments be made into a Q&A. So:

From the Cloud of Daggers spell (others have similar wording)

You fill the air with spinning daggers in a cube 5 feet on each side, centered on a point you choose within range. A creature takes 4d4 slashing damage when it enters the spell’s area for the first time on a turn or starts its turn there. (PHB 222)

What does "... when it enters the spell’s area for the first time on a turn or starts its turn there" mean?

Answer 1

April 2016's Sage Advice expressly defines how this phrase operates and names Cloud of Daggers as one of several spells to which this definition applies.

In summary, a spell like moonbeam affects a creature when the creature passes into the spell’s area of effect and when the creature starts its turn there. You’re essentially creating a hazard on the battlefield.

Furthermore, it is stated that such spells do not damage targets when initially cast.

So this is how it works:

1. Daffy the Wizard casts Cloud of Daggers atop a mighty gorgon. The gorgon takes no damage. (You could say it is 'undeterred'.)

2. Garrosh, an orc barbarian, pushes a murloc into the Cloud of Daggers. The murloc takes damage (and shares the space with the gorgon).

3. The gorgon takes its turn and starts within the Cloud's effect, thus it takes damage. It wisely moves out of that area.

4. The murloc takes its turn and starts within the Cloud's effect, thus it takes damage. It chooses to remain in that space. On its next turn, it will take damage again. (Must be quite the murloc to still be alive.)

Answer 2

I rule that the targets of these spells only take damage once a turn. Additionally, they don't take damage on the turn when the spell was cast, as per this Sage Advice from Mr Crawford (thanks Airatome).

Consider the following example (from another answer here), a wizard (W) and a barbarian (B) are fighting the Evil Bad Guy (E). The initiative order is W then E then B.

W: Casts cloud of daggers on the area where E is standing. E takes no damage at this time.

E: Has started his turn in the area of effect of the spell, so takes damage. He moves out of the spell's AoE but realises he's run the wrong way, so he moves back into the AoE and out the other side. He takes no damage at this time, because he's already taken damage from the spell once on this turn¹.

B: Runs around to E, grapples him, and carried him into the AoE of the spell. This is the first time E has entered the AoE on this turn (B's turn), so he takes damage. B also takes damage.

¹ This is to stop cheesy exploits like using moonbeam to damage a target 30 times in one turn.

Answer 3

From PHB p.189

The game organizes the chaos of combat into a cycle of rounds and turns. A round represents about 6 seconds in the game world. During a round, each participant in a battle takes a turn.

Dealing with the last part first, "starts its turn there" is self explanatory - when the round rolls round to that person's turn, if they are standing in the cloud they take damage.

For the first part, "when it enters the spell’s area for the first time on a turn" also means what it says - if at the start of any creature's turn (including its own) it takes damage the first time it enters but not if it then leaves and reenters.

Consider the following example, a party consisting of a wizard (W) and a barbarian (B) are fighting the Evil Bad Guy (E). The initiative order is W->E->B

1. W casts Cloud of Daggers on E - E takes damage as it "enters the spell’s area for the first time on a turn" - the entering being caused by the appearance of the cloud rather than E moving.
2. E takes damage again due to "starts its turn there". Feeling that this is not fun, he moves out of the cloud. If he moved back in, would he take damage for "enters the spell’s area for the first time on a turn"? This is a DM call as it could be argued both ways (no - because you had "entered" at the start of your turn"; you were there you left now you have re-entered and anyway the "or" here means "either but not both", yes - being there at the start does not count as "entering"; you were there you left now you have entered). Notwithstanding, after this he could move in and out with impunity this turn.
3. The raging B, struck with inspiration, grapples E and moves with him into the cloud. They both take damage due to "enters the spell’s area for the first time on a turn" but B has resistance. B then lets go and steps out of the cloud.
4. W is falling down laughing and wastes his turn standing up.
5. E is now back where he was at step 2.

Answer 4

1. Remember that a round is everyone having had a turn.
2. Remember that sometimes you act on someone else's turn. (using a reaction)
3. Remember that sometimes you are moved during someone else's turn involuntarily

So...

... when it enters the spell’s area for the first time on a turn or starts its turn there.

This has several subcomponents interacting in several important ways...

• it doesn't say "on its turn" so involuntary movement may trigger, as may reactions to use the dash action or other movement reactions.
• it does say "on a turn" so that would apply also on the caster's turn, or anyone else's turn.
• "the first time" prevents force-moving the character through it twice during any one character's turn, but doesn't preclude Fred from pushing you through it one way, then joe pushing you back...
• the only time start of turn matters is for the victims - at their turn beginning.
  • This excludes taking damage on any turn but the victim's own if it remains inside
  • this excludes taking damage from movement inside (but that's not relevant since the effect on that spell is so small)
  • this excludes taking damage from it twice if you start a turn outside it

The bit about starting its turn in it is pretty self-explanatory. If, for any reason, when your initiative comes around, if the spell is still going, and you're inside, you get hit.

There's one edge case left: You start inside, and leave it, then return to the cloud. So, when you start inside, you get hit before you can move. You exit, then enter again, getting hit again as you enter. If you exit and enter again, you do NOT take a third hit.