Currently (7/13/2024), ghouls summoned by Danse Macabre will continue to attack a Knocked Out target for 0 damage and will not switch targets so long as the target remains Knocked Out.
The ghouls are immune to Demonspirit Madness. This prevents them from being driven Mad due to a failed Wisdom saving throw when the summoner wears Abyss Beckoners.
Currently (09/13/2023) the Necromancy Wizard subclass is causing this spell to summon 5 ghouls instead of 4. Spell tooltip unchanged.
The Ghouls explode when killed, dealing Necrotic area-of-effect damage. This can destroy other Ghouls as a chain reaction and hurt nearby party members as well.
Since the Ghouls cannot be controlled by the player, they can sometimes 'split' player-controlled characters into different sections of the Initiative order (e.g. Player character/Gale/Astarion/Ghoul/Shadowheart). This prevents the player from swapping between party members before the ghoul and party members after the ghoul (e.g. they cannot have Shadowheart cast Create Water before Gale casts a spell with Lightning damage). This is a potentially large downside to using Danse Macabre.