One of the most important things Luffy needs to do well in One Piece World Seeker in order to buy time to replenish health is to be able to sneak. By staying out of an enemy's line of sight Luffy can use the stealth mechanic to creep up behind them without being spotted and deliver a takedown by pressiong the 'Square' button on the d-pad to instantly knock them out. Luffy will be able to do this to almost any enemy, including bosses, making knowing how to sneak a must know strategy.
To make Luffy sneak you need to make sure you are in Observation Haki mode or have unlocked the required skill for Armament Haki mode. Once this requirement has been met push the left analog stick of your D-pad forward only slightly so that you ensure Luffy maintains a slow walking speed and approach the enemy from behind. If done correctly enemies will struggle to detect you.
If you are having trouble pulling off sneak attacks to knock out the enemy you may need the help of the following two skills. The first is the Aura Cloaking skill which lowers your chances of being detected by as much as 50 pecent. This skill can can be found in the lowest branch of the Parameters Skill Tree. The other ability that is useful for sneaking is the Consecutive Takedown skill which can be found in the middle branch of the Haki Tree. This ability enables Luffy to string together multiple takedowns if he is near several enemies that have not detected him. When the Consecutive Takedown skill has been upgraded Luffy will be able to carry out as many as five takedowns in a row before having to return to basic sneaking.
Check out our How to Grapple page to see how you can use Luffy's grappling ability as a melee attack.