Dirk, Hermes, Necryx, Jomil and Sing Lore- avert your eyes, or incur the wrath of Spuggroth the Humbled and Aflame!
I'm designing an encounter where the party is trying to confront some foes in the midst of a massive bar fight, which I'm thinking of treating as two gargantuan, overlapping swarms fighting each other (the party has a stake in which side wins the bar fight, and the encounter will grow more dangerous if their side starts losing)
For reference, the swarm ability includes the following text:
Swarm. The swarm can occupy another creature's space and vice versa
It's established that moving out of the 0 ft. reach of a swarm triggers an opportunity attack as per usual, but if I create a gargantuan swarm, it's very likely a player could begin and end it's movement while remaining entirely within the swarm.
Using the rules as written, I'd assume a character moving in this way would not trigger an opportunity attack, but it does seem a bit counterintuitive. I can't think of any gargantuan swarms in published 5e content, and this might be why, but if anyone has some insights on how to rule this, or if there was a clarification published somewhere, I'd love to hear it.