My favorite Metroidvania transformation is Quote from Cave Story (minor spoilers ahead if you never played it), which over the years became a very personal game for me. I'll never forget the first time I played Cave Story which was late 2005 on an old 1999 year HP desktop tower PC running Win '98 and a tiny 3.2 GB hard drive on a rainy day back in my home town. Going through the opening cave and then entering Mimiga Town for the first time and hearing its beautifully melancholy music was magical. I couldn't believe this was a freeware, independently made game, the visuals and music were and still are so wonderful. It instantly reminded me of the Wonder Boy series.
Quote himself may not go through literal transformations, but his transformations are emotional and thematic. Going from waking up in the Cave and being an amnesiac to discovering your dark purpose: a surface android sent to slaughter and fight the innocent Mimiga who are being experimented on by the doctor all in a quest for the evil, coveted crown which has kept the island a dark place. Gradually finding your redemptive side as you help an old lady and her puppies, making an emotional connection with Curly Brace and the ultimate thematic transformation: escaping the Cave/floating island.
About eight months after playing the game for the first time I moved away from my hometown, I was young and headstrong and for years felt like "my home town is sooooooo boring now, I need to try new things! Grrrrrr." Typical young guff. I wasn't just leaving my hometown, I was escaping my own Cave and floating away in a dragon into the clouds.
However, the reality and the challenges of living in a new town set in. Being away from my family and friends was much harder than I thought, I'll never forget the night I cried thinking I should go back right away but I thought, no I have to stick to my decision. Over the years my friends back home grew and changed and my family went through some stressful things. Even though I made many visits back to see everyone you can't keep life the way it is but ultimately they all survived. Like I did. Like Quote did. Because like Cave Story, life can be tough with some dark moments, but it's still beautiful and fun when you look for the good things and things to be thankful for.
So whenever I hear the melancholy and wistful Mimiga town theme, I get misty eyed, and for just one moment I am transported back to my hometown in 2005 with that old PC playing the game for the first time and I can live in the old, warm moments of my young life before I solemnly wake out of my brief reverie and back into the present again with all of its new joys and challenges.