I played in a highly fun and amusing session of D&D 5E at one of my local game conventions, Pacificon, and I thought I'd share and reflect. It was a game in the heist genre entitled "The Land Juggerpede" - in a post-fantasy-apocalypse setting.
What really capped the session was the climactic battle. In a classic heist genre twist, we were trying to raid a dwarven train ("land juggerpede") but there was another team of adventurers trying to raid it at the same time. We had defeated a few people, but we didn't know who was guarding the train and who was raiding it. We had defeated some prior adventurers, though.
In the climactic battle, we happened on some elite kobolds faced off against two adventurers (an elf and a dwarf). Were the kobolds part of the raiding party, or were they hired by the guards?
However, we had with us two characters with Disguise Self (my bard and my son's warlock). To break the standoff, the warlock ran into the room disguised as a defeated adventurer and simply said "Don't worry. Reinforcements are coming." Then the kobolds shot at him and the adventurers called for him to get under cover.
The next round, I ran across to the opposite side disguised as a train guard and joined the kobolds saying "Don't worry. Reinforcements are coming."
What followed was a very confusing and very entertaining 3+ way fight where even we had trouble telling who was on what side. My character used the Minor Illusion cantrip to "attack" the disguised warlock with a thrown axe. Our dwarven rogue charged in and was gravely wounded, and then played dead. By the end, the warlock and the rogue had both been taken out twice and healed twice, but we were all still barely standing along with one particularly tough kobold dragonshield. We then made a deal with him, and took the gold while leaving him his charge (a gold dragon egg).
I think system parts that made it shine were the cinematic/swashbuckling tactical combat, the player powers, and the individual initiative. I've certainly had fun in games with group initiative, but it tends to make situations less chaotic, and sometimes more chaotic is more fun.
I'd love to hear about other chaotic fun scenes with disguises, double-crosses, and mixed sides.