Undertale Promised is a fan-made adventure game set in the world of Undertale. It starts with Sans running into you on a snowy bridge, which seems harmless at first. But things go south fast when he realizes you've already taken down several monsters.
The battle isn't just about mashing the attack button. What you do shapes how the fight plays out—whether you fight, spare, or try something offbeat, each choice can steer things in a different direction.
There's also an Easter Attack Mode that cranks up the difficulty. Push Sans too far, and the fight gets way more brutal, so knowing when to back off matters just as much as knowing when to strike.

What makes this one stand out is how it takes a classic Undertale-style fight and zeroes in on Sans as the main event. The snowy setting, the weird attack patterns, the branching choices, and the multiple endings all give it more character than your average boss battle.
If you enjoy Undertale fan games, tough fights, or games where your choices really matter, this one is worth trying.