Impacts of changing all similar spells to work like Moonbeam or Flaming Sphere

Question

A few things really bothers me in this game, one of them is the fact that static area damage spells can work in many different way for seemingly no reason. What I'd call damage timing : When does an area spell deal its damage.

The main two versions I see are the Moonbeam version (assuming this answer is right ), where damage is dealt at the begining of the victim's turn. And the Flaming sphere version, where damage is dealt on casting (or on a special bonus action) and then at the end of the victim's turn. But I also found a number of spells that work differently.

To make it easier on myself, I am thinking of reworking all spells that seem to work the same :

• Create a zone of danger (that can move like Moonbeam or not like Wall of Fire) on the playing field.
• Require creatures inside of it (usually all, but not always like Spirit Guardians) to make a save to avoid damage.
• Usually only deal damage once per round if the target is free to move away. I expect any creature to move away from those spells.
  • I choose to ignore forced movement and out-of-turn movements since they are, in my experience, the exception rather than the norm due to the coordination aspect of pulling them off.

In order to consolidate and simplify the 'damage timing' of area spells, I would change them to work either on "cast&end of turn" like Flaming Sphere or "on start of turn&moving in" like Moonbeam. All working the same.

How does the rework affect common uses of the spells described above?

Examples of common uses I see are:

• As a single target damage spell (moving the zone to follow the intended target) with bonus damage if the caster can line up extra creatures.
• As way to force "willing" movement on the target. Such as to open up attacks of opportunity.
• As an area denial spell. Hopefully preventing retreat or preventing going into melee.

I assume both rework are similar enough to be equivalent, if they change the usage of the spell, an answer can highlight how they would change the uses. I assume also that forced movements are rare, but if a poster thinks I'm wrong, I would be interested to hear why as well as how it impacts the spell.

For additionnal context : Prior to this question, I was looking for a way to remember which spell work which way and, by extension, how can I create homebrew spells to fit with those already available. So while this is not exactly the main question, I am interested in an answer that can highlight how different configurations of damage timing will change how players can use the spell.

Answer 1

"On cast and end-of-turn" won't prevent a creature from moving through the affected area, so won't be as useful at preventing retreat or keeping enemies out of melee. This also makes the spell far less useful if it can't be moved, since the result is "you can move through here, just don't end your movement here".

On the other hand, "on cast and end-of-turn" effects tend to be more punishing if the creature doesn't move, hitting them twice instead of once. For contrast, if the creature doesn't leave a "start-of-turn-or-entry" effect, it just leaves the caster free to use their action (or bonus action) to do something else, and that "something else" tends not to be as potent.

For further examples of this, Flaming Sphere only hits one target each time the caster moves it, the "AoE" component only triggers if the targets don't move. And "Dust Devil" deals no damage at all unless the targets don't move.

And while forced movement is relatively rare, prevented movement is more common. For example, you can use your AoE in an enclosed space when you (and your allies) are blocking the only exits. Or you can grapple them. There are also ways to penalise a creature for moving, such as attacks-of-opportunity or spells like Booming Blade. These work well with forcing a creature to leave a space, but not so well with preventing a creature from entering a space.