The Ottoshot (or just Otto and a naming of Auto) is a fairly common move made possible by abusing various gameplay mechanics (aka Glitch Abuse). Despite the glitches, GMs verified it as legal. It allows the user to repeatedly strike with the first hit of their combo at an extremely rapid pace by attacking while going through a platform underneath.
The Ottoshot is a useful technique, and can quickly kill a monster if used successfully, but it will only ever bring the opponent to fatal status if used in PvP. In PvP, it can only be used up to 5 times, until Season 3 which removed the feature.
Although using Ottoshot is perfectly legal, it is banned from tournament use since it is classified as "Infinite Chaining", and disobedience of this rule will end in immediate disqualification.
Other Types of Ottoshot
Certain other classes have their own method of "Ottoshot".
All of Lire's ottoshot, however, requires the class to walk off the edge of a platform and shoot an arrow at the right time. The recoil of the arrow then sends the archer back to the edge of the platform, in which they can then repeat the ottoshot.
If possible, she may use both Double Jump Shot and Rapid Fire to jump to the air, and fire constantly until the buff runs out.
The Shisa's "Step" ability can easily be translated into an Otto if done repeatedly.
The Battle Mage's aerial firebolt attack can be used as an Otto, called the Firebolt Otto; however it is not as fast as a traditional Otto, and some players do not consider this a true Otto. It is used by performing the aerial firebolt attack just before touching a platform to cancel out the firebolt and jumping animation. Generally, the Battle Mage would need to be able to jump up and then back down between platforms while performing the aerial firebolt attack in quick succession repeatedly. 
Classes That Can Use Ottoshot
- Sword Master
- Crossbowman (With and without a platform)
- Arch Ranger
- Battle Mage
- Dark Assassin
- Vanquisher (Storm Pike Mode)
- Magnus Dan (With and without a platform)
- Spell Knight
- Dragon Knight
- Aegis Knight
- Abyss Knight
- Gladiator (With Jump Attack Level 2 Skill Tree)
- Prime Knight
- Seeker (OS Dash Attack)
- Awakened (Dark)