I was just wondering: In Terraria, when does each boss theme play? I know the 1st theme plays during the EoC.
You can find a list of all the tracks on the wiki. I'll list the boss themes below with quotes from the wiki on when they play.
It plays during invasions by the Goblin Army and during the fight with the Eye of Cthulhu, King Slime, Eater of Worlds, Skeletron, Lepus (Mobile), and Turkor the Ungrateful (Mobile). In hardmode, it also plays during the fight with Skeletron Prime and Duke Fishron.
It plays during the fight with the Wall of Flesh and The Twins, which suits them very well.
It plays during the fight with The Destroyer, as well as invasions by the Frost Legion. As of 1.2, this track is also played during the fight with the Brain of Cthulhu.
It plays during the fight with the Golem and Pirate Invasion.
It plays during the fight with Plantera.
It plays during the fight against the Queen Bee. This track was added in the 1.2 patch, along with all the possible situations it plays in. This theme was originally exclusive to the console edition, where it is used differently. In the console version, it is used in the fight of the Eye of Cthulhu, and Ocram.