BATTLANTIS / Konami / Arcade
Konami transports Space Invaders to a medieval fantasy world with this one, and also kicks it up a notch with enemies more aggressively trying to overrun your position, some neat-for-the-time graphical scaling effects and even periodic boss battles.
This was apparently quite a rare release, given that the only cabinet I could find was sold on Etsy of all places, and there's only five registered owners of circuit boards over at the International Arcade Museum. I went to tons of different arcades as a kid in the '80s and '90s and I never saw it in the wild anywhere, had no idea it even existed until MAME added it to their roster.
Anyway, it's a really nifty idea, but it doesn't take much playing it to see why it didn't become a beloved classic. It's got far too many cheap moments, with the worst being this shield-toting alchemist who pops out on level 4 and lobs a Spread Shot of bombs at you, requiring pixel-perfect precision to stand in between them as they land or you die and have to start the whole sequence over. There's also a lot of moments where enemies will arrive at your position simultaneously on different sides, and it's impossible to kill both of them before one gets up on your platform. If you don't have the fully upgraded weapon that shoots side to side, an enemy making it onto your platform is guaranteed death.
Battlantis actually had a surprise re-release for the Microsoft Game Room service a few years ago, but since that thing is no longer available, MAMEing it up is the only way to play it until further notice.
* Battlantis Fan Site
with ripped soundtrack