"Due to the close proximity of the insects to each other the whole swarm explodes into a mist of blood and parts of elefant carcasses raining down all over the battlefield. Time for everyone to roll..."
Buzzkill DM: Locusts, even under the loose control of a druid, are not intelligent enough to be "willing" to be transformed, so they can't be targeted by animal shapes, rules as written.
Better DM: That's cool as hell. Do it.
Best DM: I'll allow it, but you better start watching the skies from here on out. If you can do it, then the enemy can too.
Thinking quickly, the BBEG casts Berserker and Shield Bubble as AoE spells in the sky above him.
While he does suffer considerable damage once they all hit the ground, the enraged elephants do not. Now the battlefield has hundreds of larger-than-life bucky balls rolling in every direction.
Each player must flip a coin before every turn to determine if they successfully dodged the latest pachydermian steamroller barreling towards them with reckless abandon.
I mean the spell says it conjures locusts. I don’t see any reason to think otherwise.
The second bit is more interesting since locusts almost certainly aren’t capable of understanding or consenting to a spell effect and don’t know they would die if they participated. But I would rule all creatures that can’t understand enough to consent automatically reject such magic.
There's nothing in the verbiage that lets you fight off the insects in any way. Fireball it? There's still locusts everywhere. Didn't even thin out the cloud.
Maybe if a summoned swarm of insects had mass charm or mass suggestion cast on it to cause the insects to obey, I'd allow that although it clearly bends the rules even at that point.
Animal Shapes, as another pointed out, has a range of 30 ft, so either the elephants can't fall as far or more shenanigans need to be added. (Distant Spell, if it can be obtained, still only makes that 60 ft.)
They're probably all much closer together than an elephant length right? So them all turning into elephants would cause the size of the swarm to instantly and violently expand, possibly ejecting some of the outer ones at great speed and endangering everyone within a considerable distance.
So you're saying it's a pressurized pachyderm propulsor? An elephant ejecting explosion? A hephalump hurling horde? I like it, and I definitely like the potential for kinetic chaos.
It’s not perfect, but my ruling would be the “swarm” of locusts count as one animal, so they’d still get an elephant falling on the BBEG, but it’s not ridiculous.
Insect swarm creates a magical effect, it doesn't summon literal bugs. And before you call me a buzz kill, it's kind of lame to try and essentially skip the encounter I spent time building.