Hawk Diesel
Adventurer
Next time, just change the way its described. DM created enemies and monsters don't have to follow the "rules." Balance is for the players so none of them can monopolize the spotlight. Anyways, you could have described it as the cultist using their demonic powers to charge the lighting within their throat until it visibly moved down their chest, through their arm, into their fist, which they then attempt to discharge into the paladin. You could then treat it like an enhanced shocking grasp, turning it into a spell attack rather than a dex save. Or, if you wanna maintain the dex save mechanic, you could state that through magic from their demonic pact, they have learned to transform their breath weapon into an ability similar to flamestrike.
It's ok to change enemy abilities on the fly to keep up the challenge and make sure the players stay on their toes. But you also need to balance that with player fun. If this player's paladin was surrounded like this, it probably didn't feel fun for him to be surrounded like he was and singled out. Of course, this depends on if it was his choices that got him into the mess and where the otger players were.
Also, it can be fun if the enemies are not always infallible. I think it would be totally in line for the cultists to release simultaneous breath weapon attacks, potentially sacrificing themselves, for their demon patron to get an opening.
It's ok to change enemy abilities on the fly to keep up the challenge and make sure the players stay on their toes. But you also need to balance that with player fun. If this player's paladin was surrounded like this, it probably didn't feel fun for him to be surrounded like he was and singled out. Of course, this depends on if it was his choices that got him into the mess and where the otger players were.
Also, it can be fun if the enemies are not always infallible. I think it would be totally in line for the cultists to release simultaneous breath weapon attacks, potentially sacrificing themselves, for their demon patron to get an opening.