Those are content DLCs:
Heart of Gold
My Pet Dungeon
Under Games

Basically any DLC labelled as an expansion

Heart of gold is a great set of missions, with some new mechanics to toy with. Pet dungeon is an homage to dungeon keeper 2, where you have general freedom but each mission has a score you need to reach for "victory". Undergames has a hate love relationship with the community. It's designed like skirmish in that you always play against other underlords, and there's difficulty settings, but with a twist in that you choose an underlord to play that has unique benefits and downsides, and a unique roster. I found it a lot of fun to play at normal difficulty, and with some practice I managed to beat it on master with one of the underlords, but generally beating master requires a lot of skill and/or practice. Some people even find normal to be unusually difficult. I would definitely suggest not playing Lamash if you wanna try to beat it at high difficulty. He's been nerfed hard through previous patches and can't keep up with the other underlords.