The king has one special attack as you already know of.
Every 10.3-10.4 seconds, the lizard king stops running and smashes the ground 8 times.
The first hit deals very little damage, like 5-10.
The damage increases with each hit and when it reaches no. 7 or 8, it deals 3-digit damage.
And the closer to him, the higher the damage.
If you pay close attention to Bonehart's health bar in the following gif, you'll see the damage increases with each hit.
And it took the lizard 6 hits to kill a Bone Golem (160 HP).
The damage of each hit went like this: 9-13-21-34-53-83-120-166.
I tested again with other heroes and put them closer to the lizard king.
Dante a very short distance away, not in melee: 10-16-23-37-59-91-131-??(he died on the 8th)
Grawl in melee with the king: 10-15-24-39-62-96-138-191. After hitting Grawl 8 times with that special hammers, the king attacked with his normal tongue attack.
When I put Bonehart distant (the lizard around the middle corner, Bonehart down there with the Dwarfs) from the lizard, the special attack's damage was 5-7-12-20-30-50-70-100.
