Ambles

 Ambles is a sentient tree monster found as an easter egg if one digs with a spade fifteen blocks north of Falador's north gate. Upon digging in this spot, he will appear and yell 'Oh, not again!' before attacking the player, dealing 50 damage, and despawning.

Trivia

- Guards will occasionally mention a 'grumpy old tree-man' when you talk to them, in Falador. Apparently, they ocassionally dig him up for fun.