A ground area-of-effect as I discuss it might be a volume, and it might be movable.

The main way 5.0 does a ground aoe is with this text:

The first creature statement often has conditions- some affect only creatures you choose, some affect creatures of a type, some effect all creatures. Objects aren't included in this, and if you want your ground aoe to fuck them up you need a whole different clause, likely triggered by something about your turn (you, the caster).

The "(is affected)" part can be basically anything the spell does.

So why is it like this? My explanation, which may or may not be related to what the dev's would say if asked, is that this realistically models the round as simultaneous. Spells that do this usually affect everything you cast it on because normally creatures don't move except on their turns, but it has the dual desirable effects of being a real threat on each turn (the turns of a round are happening kinda at the same time, remember). So if there's some burning cylinder and it's your turn, you want to get out of the burning cylinder if you're in it (taking damage at the start of your turn, but hopefully preventing taking damage at the start of your next turn). If you aren't in it, the mechanics above provide you motivation to not just run through it.

This mechanic isn't perfect. Playing just by the fully defined rules, some important monsters can move at the end of another creature's turn with a legendary action, meaning that this class of enemy is a poor choice for ground aoe, and the fact that they are pretty fast and zippy doesn't seem a fully satisfying reason for this effective immunity (to me at least). While not as lame, players can also cheese this- either with fully defined rules interactions like thorn whipping your buddy out of something much more damaging than thorn whip before it has a chance to do a damned thing, or simply using the partially defined set of "I'm gonna drag him and he's gonna let it happen" type actions. These don't trivialize these effects like legendary movement actions can, because the players at least have to spend a real resource (an action) to do them, which seems like the type of interaction that the game wants everyone to engage in.

Finally, there's the fact that you do have to remember to resolve the effect- mostly really easy because you've drawn it on your map- and of course it slows the game down a bit because every single turn now involves like, "ok make a save. Uh, it's a wisdom save right lemme just yup wisdom. Ok you failed? You take (rolls dice) 14 points of damage and you're restrained. Man I forget, we just looked it up though ok you can't move you have disadvantage on attacks, attacks against you have advantage and you have disadvantage on dexterity saves..."

For this reason, ground aoe are usually concentration if available to the PCs or only available as one thing at a time if some monster power.


Here's some spells that work like this:
black tentacles (formerly Ebon's), blade barrier, cloudkill, cloud of daggers (arguably neither a cloud, nor daggers), control water (when you make a whirlpool), control winds (when you make a downdraft), forbiddance, hallow, healing spirit, moonbeam, prismatic wall (for the radial blind effect), sickening radiance, sleet storm, spirit guardians, web

Here's spells that lack the "enters the area for the first time on its turn" clause, which generally means these hazards can be passed through harmlessly by creatures on their turn, and are only a concern when placed initially or if a creature is knocked into the area by enemy action (if you walk into it on your turn, it's because you have enough movement to get out so you don't end your turn there):
gust of wind (I'm not really sure why), maddening darkness (This is probably because it's a 60 foot radius sphere, which is massive), maelstrom (Not really sure why, it's basically another whirlpool like control water), manifest lesser void (formerly "hunger of hadar"- this also has an end of turn effect, and it creates difficult terrain, so someone who skirts the edge on their turn can get out without damage, but still has to deal with the extra movement cost), primal ray (The lava ray option of this custom spell can heat a small area, and I didn't want it to be overly concerning to those passing through because that's not really what the spell is about), spirit shroud- As a mobile point blank aoe, this would be too punishing to melee attackers if it triggered when they close in on you, and it would be poorly defined given that it's a speed debuff.

There's one spell that does stuff when you move it over them, and it's the 7th level spell color=#0000BF]whirlwind[/color] from Xanathar's. This spell is important enough to parse carefully if anyone casts it, and it seems like it would be fun to hit the players with. Players would probably only find this spell useful if up against 3-6 rather powerful creatures that don't have a lot of inherent fast flight- like another adventuring party.


Now onto the 5.5 piece- this doesn't affect this game at all. Below this point is just me bitching and ranting.
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Baldur's Gate 3 had some spells that did their effects when you moved it over enemies on their turns- the main culprit being moonbeam I believe, which makes it incredibly powerful in closed spaces. Here's the two moonbeam description parts:


So you can't "sweep" this around, you position it over an enemy or in a spot you want to deny passage to (with the threat being radiant damage). But the 5.5 spell becomes:


Way more words about this, but this version of the spell you can sweep over the battlefield with your action and you have to track it in real time, noting who gets tagged, how much movement you have left, etc. None of this needed to be tracked in 5.0, where you just move it anywhere within 60 feet and the path doesn't matter. Now you have to walk it around friendlies and it becomes a huge deal to smack the entire enemy team with it.

You can readily find forums engaged in a spirited debate about this very massive buff to the spell, with plenty of DMs nerfing it and players raging as a result. If I wanted an effect like this, I'd have a rider where as an action you can move it and also choose like some creatures within ranged to take radiant damage right then, keeping the no-clip version from 5.0. That would be the proper 5e way to make such an effect, and it could be described better as well. I believe the 5.5 version to be terribly designed- and what, exactly, is the description of this event? This moonbeam is now zipping around like a weird laser every round tagging every enemy at least once, whereas before it simply moved to its final position over six seconds. I consider this spell's change from easily understood and pretty powerful to weirdly powerful, resolving with an otherwise unknown and slow-to-run mechanic, and being impossible to describe without it sounding retarded, to be yet one more reason why I won't run a baseline 5.5 game ever.