Frost dragon

Imagine a castle like abandoned building engulfed in ice in an ice spikes biome. When the player enters they first encounter some undead mobs like the strays and as the go deeper they eventually see a giant frozen frost dragon and after doing something to defrost it (like use a fire aspect sword or flame bow) it wakes wakes up in a fiery explosion that blows the roof of the castle off and the battle begins and as a reward for defeating such a mighty beast the player gets the dragons tongue which they can use to craft a new type of sword that applies ice damage to enemies or freezes them after 1 or 2 hits.