The Yeti King is a mini-boss found only in special Yeti Kingdom levels in the Ice Caves.
He is capable of causing a lot of destruction to the level and killing the Spelunker instantly using his mighty roar, blasting the Spelunker through the air and causing avalanches.
He is always found with a group of several Yeti that make him difficult to approach safely.
Because he is considered a mini-boss, killing him unlocks eight Deathmatch Arenas.
Unlike regular Yeti, the Yeti King is actively aggressive and will attack the Spelunker on sight, making him a much more dangerous enemy.
He will pursue the Spelunker if they try to run away, using his roar to cause ice blocks to fall from the ceiling as icicles that will crush anything they land on. Any character that is in front of the Yeti King as he roars will be knocked back and stunned, but won't take any direct damage. Beware though - his breath can still affect the player several blocks above him on either side, and will likely be stun locked to death or sent flying into something more deadly.
The Yeti King can be relatively easy to deal with as he isn't actively hostile to The Spelunker, but there are two factors worth considering. First, he always spawns with a horde of smaller Yeti, and secondly, his roar can cause avalanches of ice blocks to fall, crushing anything they land on.
The best way to kill the Yeti King is by catching him in a bomb explosion, which will kill him instantly. If you're lucky enough to have a UFO spawn near him, you might be able to throw a projectile at it and have it crash down on him and explode. You can also use a Shotgun, should you be lucky enough to have one, but be warned that he'll take more than one blast to be killed. However, a well-timed shot can sometimes push him into his own avalanche, insta-crushing him.
Additionally, bouncing on his head repeatedly is an excellent tactic as he moves quite slowly and has no way to shake you off, assuming you can move through the hordes of Yeti to get close enough to him.
As long as you can chain jump reliably, he should die with little trouble. Thrown objects are also effective, especially as they can cause a chain reaction with the hordes of Yeti around him. In fact, stunning a Yeti and using it as a projectile is also very effective. His width and slow movement means that most thrown objects tend to hit him multiple times as they move through his hitbox.
Sometimes when he roars, the ice that falls will crush the Yeti hordes around him.