A Pokemon stealth game. Preferably Mystery Dungeon, where you go on high-risk, high-reward missions as a Pokemon. Unlike the regular Mystery Dungeon games, the goal is to avoid your enemies, not fight them.
You use the darkness, your tools, and maybe a bit of teamwork to achieve your goals. In this game, you are not invincible. In fact, if you face more than one, you may want to run rather than fight, because they can quickly outnumber you as they summon their friends.
The things to watch are:
1: The sound of your footsteps on different surfaces.
2: Your visibility.
3: Advanced AI that can see, hear, feel, and think. They also have unique strategies for defeating you, should you get caught.
4: If you're strong enough, and if the enemy pokemon isn't too heavy, you can drag its body in the shadows, where no one will notice it.
5: On the higher difficulty modes, you face more obstacles and objectives. Things like not being allowed to defeat certain pokemon, or maybe you have to "ghost" your way through the missions. I think that means not getting caught at all.
6: The Pokemon's "patrol" routes. Sometimes two or more pokemon cross paths, and if you pick the wrong moment to sneak by, you're in trouble.
7: Opportunities for pokemon types. For example, if you're a water type, then you can use a water-based move, and do things like douse torches to create darkness, blast away fragile walls, and sometimes (if you're powerful enough), propel yourself backwards for a quick escape.
There should be a guild, and a guildmaster; only the missions are more delicate, and require special skills to complete. Since the missions require special skills, you will recieve less of a penalty with the guild training costs (which was 9/10 of all the money you earned by completing jobs), and you get to take enemy treasures and items.