Welcome back! Continuing yesterday's initial attempt, we're going for 30 video game songs in 30 days, each representing a different theme or subject. Challenge mode: No repeats in games, or game franchises. (I'm going to allow non-canon mash-ups, for example Super Smash Bros., under the same specific rule that I cannot repeat games from that specific franchise, while still allowing characters, for example Samus, to be considered as separate franchises.)
Day 2's category is "Opening level music", and for this, I went with the iconic classic: Castlevania. I had to. "Vampire Killer" is itself so iconic, and it truly represents the whole series; for a song on the original NES hardware, it slaps. (It's probably even better on the Famicom Disk System! I can't find that one.) Hard to find a song like that.
In fact, I'm going to break from the original point of the challenge and make an honorable mention in this case: Castlevania II: Simon's Quest. Similar to "Vampire Killer", "Bloody Tears" does a magnificent job of representing the entire franchise from the opening frames of the game, this time the second. I would be remiss if I didn't at least bring it up.