Green Knight's element is Poison. All poison attacks do three hits of DoT. However, some enemies such as Cult Minions, are highly resistant to Poison and are immune to its secondary effects. Which makes it about as effective as Fire and is a relatively good element. Another unique characteristic about the Green Knight is that his heavy attack speed, compared to other characters, is rather sluggish, and it irritatingly can cause you to adapt to his heavy attack in juggling unlike the other 30 characters.
Damage/Hit: Base Magic Damage x 0.5 + Poison DoT x 3
A poisonous cloud pillows forth, knocking over any enemies it hits and poisons them. The poisoning damage over time effect makes this pretty powerful and potentially superior to fire. Each upgrade level adds to the range and to how many max hits the spell can inflict on an enemy that is not knocked over by it. This spell's collision is a bit odd in that it can go through a decent amount past terrain obstacles such as walls, pits, and the line of the volleyball game, albeit it won't fully go past the line unlike Industrialist and Fencer's splash attacks, which fully can.
A ball of poison. The Poison DoT is rather nice in killing enemies quicker; more so than Fire DoT. Since Green Knight has a different YY/△△) than all of the other 30 characters in the game, assuming you know how to levitate (XYY/□△△) Level 8 required) + spellweave (RT+Y/RT+△) (10 points allocated into Magic), Green Knight can cast 5 slanted Magic Projectiles while still in the air, unless you also know how to Slow Levitate (RT+A AA XYY/RT+X XX □△△) in which you can cast slanted Magic Projectiles infinitely and easier.