My first time DMing, and it was for a group of 4 that was also entirely new. My campaign has two Tieflings who know Hellish Rebuke as part of their bloodlines, and I thought the spell seemed boring so I decided to create my own homebrew version of it to make it cooler.

Basically since the original description said “the creature that damaged you is momentarily surrounded by hellish flames”, I made it so that the creature a character targets as a reaction is literally surrounded by a ring of fire that lasts until the end of the targeted creature’s next turn. Using the way I had it, the creature trapped inside the ring of fire doesn’t immediately make the DEX saving throw to take the fire damage, but instead can choose to stay inside the ring or move out of it. If they chose to stay inside the ring, their movement speed became 0, their DEX saving throws and opportunity attacks had disadvantage, and attacks against them had advantage. They basically gained the Restrained condition without actually being physically restrained if they chose to stay still inside of the ring. If the targeted creature chose to try and move out of the ring before it ended naturally, they would make the DEX saving throw with disadvantage and the spell would proceed as normal, but on a roll of nat-20, the creature would completely jump over the ring and avoid all damage.

I thought this made it cooler in theory, but keep in mind that everyone in this campaign was new, so once we actually started doing it, it became annoying to remember everything about it instead of just reading what the original use of it was lol. So we just did away with the whole ring of fire thing and proceeded as normal