For the For the Bell Tolls is an action adventure game for the Game Boy. It is a precursor of sorts to The Legend of Zelda: Link's Awakening, in that the game engine of Frog Bells was used for Zelda. One of the characters of Frog Bells, Prince Richard, is even in Links Awakening in a minor role.
This isn't the only aspect in common between Zelda and Frog Bells. Frog Bells features an overworld to explore split into squares, dungeons to get through, an inventory to find and enemies to battle. That's where most of the similarities end though, as Frog Bells does most of these things it's own way.
Battling in Frog Bells requires you to simply move into an enemy. You'll jump into a cartoon smoke cloud and trade blows automatically until someone dies. Progressing in the game requires you to find hidden items to upgrade health, power, defence and speed - basically, battles are more about problem solving than combat skill. Dungeons in Frog Bells are different too - they're all side scrollers and involve more platforming than Zelda. There are still plenty of puzzles too, many of which make use of the main characters ability to transform - touching water turns you into a frog who can jump very high and walk underwater, but can't really fight unless the enemy is a bug (in which case they die instantly as you eat them) and eating a snake egg turns you into a snake who can't jump at all, but can slither through tight gaps and turn weak enemies into blocks. The human form can push these blocks and fight better but has a weaker jump than the frog.
The story of Frog Bells is very silly and light hearted too. You know the game is going to be a bit quirky at the start when your prince gives away 8999999 coins to buy a boat to catch up with his rival, then gives his last 1000000 away to a small child for giving him some wine. It's OK though, you just pull out another 1000000 out of nowhere. Money is actually quite a big plot focus as a lot of important plot elements require you to find several million worth of coins - luckily, finding it is all plot driven, no grinding for cash necessary (except for buying new shields along the way).
The whole game continues in this light hearted manner - you gain a helmet that lets you talk to frogs, mind control a mammoth, visit 'nantendo' HQ and meet people working on modern computers despite the swords and sworcery setting - it's all very fun. The difficulty is mostly fair low, besides a few peaks and the graphics are functional and pretty nice for a game boy game of it's era (1992).
There are some flaws - dying sends you back to the last town you visited, and replaying the majority of a dungeon over because you fell into an instant death pit is infuriating. The music is servicable but the tracks are too short and the looping can be grating. On a couple of occasions it's not clear where to go too.
That said, they're all minor flaws on an incredible package for Game Boy. The fact that this was never officially released in English back in the day, despite being released in the Game Boy's prime is a travesty. There's very little here that wouldn't have been approved by Nintendo of America either - a bunny girl here and there, 'wine' as a healing item and a few drunks at a bar - easily replaced with a classic 'coffee shop'. That said, the recently released fan translation which I used to play the game is great, and it feels very much like a solid translation of the era - simple, but fun and functional.
I highly recommend Frog Bells. It's should be known as one of the defining classics of the Game Boy, but weird localisation decisions stopped it achieving the recognition it deserved. It's only a 5-8 hour romp, but every bit of it is a joy to experience. Play it!