It was christmas. We (my family? The others weren't clear at this point) were unwrapping presents, and I got this video game, apparently similar to the Fable series (which I've only briefly encountered, never played).
I started playing the game, and someone was watching over my shoulder. An older female figure, almost like a big sister - which I don't have. Could've been representative of my mom, but...wasn't her.
The game had multiple settings, but the one I chose was Atlantis. She said "Ooh, that's a hard one." I was the leader, and I had to decide which path the people of atlantis were going to take: research and self betterment, or building up an empire to conquer others. It was hard because my second in command really wanted us to militarize, so every choice I had in our conversation involved trying to avoid giving in to his desires. At one point I decided we would focus on naturalistic research - starting with the surrounding sealife. At this point, the person over my shoulder said "Uh-oh, bad choice!"
Then the game became real. This happens often in my dreams, where it's alternately a game I'm playing and something I'm actually living. I was now the head researcher instead of the leader. That female figure was still there, now my research assistant. She kept making helpful suggestions, and cautioning me against doing the wrong thing.
At one point I was investigating the behavior of some sealife (I think they were jellyfish? But there was something mammilian, too. There were lots of creatures all at once, like an aquatic version of the 'can't wait to be king' scene from the lion king.
I was starting to get silly with power for some reason, and teasing the animals. Then suddenly they were sentient, and began attacking me. The jellyfish were jumping out of the water trying to sting me, and I was jumping around on pillars in the water trying to avoid them. Basically, they were saying humanity were pests ruining the world, and they were going to take it back over.
The only other thing I remember...is that the whole city was covered by a giant glass dome held in a sort of organic support structure, which was covered in barnacles. At the end of the dream, I was watching the city from an external, detached view...as it caught on fire, and the glass shattered and fell.
Also for some reason I knew that the glass dome had been created like blown glass, but for its size, also like a hot air balloon. I don't know if that's physically possible, probably not for weight/size/speed of growth/power of fire considerations - but that's how it was in the dream. Glass blown with a big flamethrower. Shattered by jellyfish.