Hero on the Halfshell
“Wealthy noble Teledji Adeledji has had his prized pet, a rare gil turtle, kidnapped by ruthless bandits who seek a sizable ransom for the gentle wavekin's return. Always a man of principle, Teledji Adeledji has decided that instead of caving to the bandit's demands, he will offer the ransom to anyone who can safely retrieve his pet from the clutches of evil.
After weakening the gil turtle, slay fire sprites and use their cores to light a special herb on fire. The smoke released should be powerful enough to put the creature to sleep, but only if the turtle is close enough to the flames.— In-game description
Hero on the Halfshell is a level 15 guildhest introduced in patch 2.0. It intends to teach basic boss mechanics.
Guide
Gil Turtle
In Hero on the Halfshell, you are required to capture a giant turtle mini-boss named Gil Turtle.
Before you start the fight, locate the environmental object Herb Patch in the boss room. You will need to interact with it later to capture the boss. When you start the fight, defeat the Amateur Raiders and Efts, and have your tank take the Gil Turtle's aggro.
After the turtle has taken some damage, a Fire Sprite spawns. The party should immediately stop attacking turtle and kill the Fire Sprite as soon as possible. Afterwards, pick up the item that it drops, and interact with the Herb Patch to burn it.
The tank then needs to pull the turtle into the burning Herb Patch to put the turtle to sleep, clearing the duty. Once the turtle is in position, it is very important to not attack it, as doing so will wake it up again. The tank should completely un-target the turtle, to ensure they don't auto-attack it.
If the Gil Turtle is accidentally killed, the duty will fail.
Loot
Reward: 
1,510 experience, 
80 gil