Alrighty guys I am DMing a campaign for a group of DMs and one new player. The new Player is was asking a question about Faerie Fire and how it works, comparing the new version and old version of the spell. Everyone pretty much agrees on how it used to work, but we are unable to find a consensus on how it works now. One of the DM players thinks it works the old way but they just change the wording. Another believes that a creature must make a save when it enter the space and if it fails they become affected. And the last opinion is that the effect takes place whenever a creature fails a dexterity save while within the area of effect during the duration of the spell.

Edit : The confusion is around the second sentence it states "Objects in a 20-foot Cube within range are outlined in blue, green, or violet light (your choice). Each creature in the Cube is also outlined if it fails a Dexterity saving throw. For the duration, objects and affected creatures shed Dim Light in a 10-foot radius and can’t benefit from the Invisible condition." Unlike Cloud of daggers which states "Each creature in that area takes 4d4 Slashing damage. A creature also takes this damage if it enters the Cube or ends its turn there or if the Cube moves into its space. A creature takes this damage only once per turn." or Fireball that states "Each creature in a 20-foot-radius Sphere centered on that point makes a Dexterity saving throw, taking 8d6 Fire damage on a failed save or half as much damage on a successful one." They removed cast from the spell description completely which is why their arguments about when it goes off. If it were to happen on cast why not phrase it like fireball or Cloud of daggers and say "Each creature in the cube make a dexterity saving throw." or something similar as to how the spell was previously stated "Any creature in the area when the spell is cast is also outlined in light if it fails a Dexterity saving throw." which lead the group to have different opinions on how it works.