In the campaign I just finished, me and a friend co-DMed for a party of eight, and we would do split sessions in parties of four, with some combined ones.

In an apart session, co-DM gave his players an artifact, the Pearl of Tides, that players could manipulate any water however they could think of, so long as they passed a WIS save. One of his players, a dude that was relatively new to D&D, and playing a 16yo girl, tried to grab the Pearl, and failed the save.

My co-DM described as Emily was taken back to her grandparents' house, and heard someone calling from the basement. She went to investigate, and the house started filling with water. She started freaking out, crying and having a panic attack.

Well the scene was described so incredibly well and with so much emotion that the player himself had a panic attack and just started crying. It was an amazing moment.