Childhood Revisited - #21 - Teenage Mutant Ninja Turtles III - Radical Rescue
3Alas, the last of the Game Boy trilogy of TMNT games. And it is, by far, the best one.
Radical Rescue was actually made by a lot of the same people who would later go on to make Castlevania: Symphony of the Night at Konami. And you can really see that heritage in the game. Instead of linear left-to-right scrolling, you get a fully explorable open map, with progress being gated by obtainable skills. Classic Metroidvania style.
The bosses are also kind of hard and you really need to learn their patterns. So... yeah. Bit of a fail here, I apologize.
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The game has never come out on any digital service (probably because of licensing rights), so your best bet is probably Ebay. It's a bit more expensive than your average Gameboy game, but still affordable.