Ninja Gaiden Shadow
Although underpowered, even in comparison to the Nintendo Entertainment System, the Game Boy did achieve quite a following, building up a substantial game library over the course of its fifteen years of life. Every major game company made attempts, however successful they may have been, to get their major game series onto the Game Boy. It was the system to own if you were young and lived in the 1990s, and game companies wanted your money.
Tecmo had a winner on their hands with the Ninja Gaiden series, with three successful games in the run on the NES. A port to the Game Boy was overdue, but instead of handling the development in-house, Tecmo farmed out the game to Natsume. They had already been developing their own ninja game for the Game Boy, based on their own title Shadow of the Ninja from 1990, so they just repurposed that game's conversion into a Ninja Gaiden game, and thus Ninja Gaiden Shadow was born. And yes, we see what they did there with the title.
Shadow only bears a passing resemblance to the rest of the Ninja Gaiden series. Ryu does still have his sword, as well as a single ninpo spell he can cast (the fire wheel), but otherwise he feels decidedly less impressive this time around. There aren't any shadow clones (despite the "Shadow" in the name), no other special attacks, and he can't even cling to walls this time around, a trademark feature of the character. He can cling to overhangs, though, and curiously gains a grappling hook he can use only in this adventure.
Some of this can be explained away as this game is a prequel to the rest of the series so of course Ryu wouldn't be as powerful here (an explanation that works "in game" but would still disappoint players). Of course, the real reason Ryu feels so off is because he plays more like the two heroes from Shadow of the Ninja, now, who had swords and could cling to overhangs. He's basically following their mold, making this a kind of hybrid between the two series. Again, the title and it's "pun" seem fairly appropriate when viewed from that angle.
The game itself isn't that bad. It's actually fairly forgiving for a Ninja Gaiden game, without all the instant death pits you expect from your free-wheeling, constantly jumping character. The emphasis here is on much more methodical play, killing enemies before they damage you and taking your time to see all the traps and tricks the game has in store. There are also frequent health drops from ninpo jars, so even if you do take damage you'll more than likely be able to heal up after.
Despite the emphasis on action over platforming, though, the bosses are fairly one-note affairs. Most of them feature simple patterns that are easy to learn, so avoiding damage from them isn't that hard, so long as you continue to pay attention. That can be a problem, though, because with the lack of additional ninja spells to learn, you're find yourself having to slog through long fights where, in other games, you could simply layer on the damage. Ryu has to be good with his sword because, due to limited ninpo and only one spell, you will mostly be relying on your melee combat to take out the beefy warriors.
Said warriors are, by and large, robots and mechs (which makes them much friendly to European audiences and the censorship that used to take place in that region). The entire game, in fact, is painted with a sci-fi brush, as if it drew inspiration not from the earlier games but Ninja Gaiden III. That's a curious aesthetic to give a prequel, all things considered, but it does look pretty damn good on the Game Boy hardware. The graphics are crisp and clean and it's easy to see Ryu against all the chaos.
Ninja Gaiden Shadow is a curiosity, to be sure. The story of its development is probably more interesting than the actual game, but for a little Game Boy title it's not bad. It wasn't good enough to warrant a sequel on the Game Boy, mind you, but for a few minutes to get your Ryu fix, it did the trick decently well.
Similarities to Castlevania Games
It's fair to say that this game has much less in common with Castlevania than Shadow of the Ninja, of course. This deep into the Ninja Gaiden series we've strayed far from direct connections to Castlevania as Ryu gets looser in his adventures, forging his own weird and random path.
That said, the grappling hook does put us in ming of Simon Belmont and his whip, or even similarly for John Morris. Both of those heroes could latch on to (select) surfaces with their whip and use that to get to different areas. Really, though, the grappling hook feels more akin to the item, and action, from Bionic Command, just with the addition that Ryu can actually jump in this game.
In anything, there's a shared fact here that the first Game Boy iterations of these series -- Ninja Gaiden Shadow and The Castlevania Adventure -- feel like rough drafts for how to take the games and put them on this small hardware. Both are stripped down affairs that lose any of the features people are accustomed to from the games, creating titles that look like their brethren but don't play anywhere near as well. Of the two Shadow fairs better, but this still is a minimal title in comparison to even Ryu's NES adventures.