The latest version of the tier list can be found in the wiki's official Discord server, which can be joined by clicking the module on the right hand side of this page or using this link. A character tier list for both arena and campaign mode can be found in the "community-tier-lists" channel on said server.
The tier list is created by averaging everyone's tier list from the Discord server. Anyone with the Knight role can make a tier list.
Keep in mind some characters are reskins of other characters with absolutely no differences, so their ranks have been combined on the tier lists.
Scroll to the bottom of the page for a general explanation of the criteria.
Generally, the tier lists are based off a highly leveled character on insane mode. Some characters accel further than others in early game, particularly due to powerful starter Weapons. However, once a player reaches insane mode, they are usually a high enough level to obtain any weapon, which is why starting weapons are not put into account.
With that in mind, a general rule is that characters are ranked solely off of their magic attacks, with two exceptions. Alien cannot change his starting weapon, and Green Knight has an abnormal heavy attack. Other than that, the tier list mostly focuses on a character's splash attack, as that is usually the most unique aspect of a character. Magic Jumps, Projectiles, Air Projectiles, and Elemental Infusions all tend to be very similar. A good splash attack serves either both or one of these purposes: the ability to manipulate crowds, or the ability to slay bosses and large enemies quickly.
A good crowd manipulator usually high knockback, high range, the ability to stun and/or the ability to damage regular enemies quickly. High knockback allows characters to push crowds back easily to take off pressure in close call situations. High range allows characters to simply attack more enemies at a single time, since splash attacks have the ability to hit anything that lands in its hitbox. A good stun splash is usually seen as the defensive alternative to a high knockback one, as it can help group up a crowd to reduce pressure and setup combos. Crowd damaging characters are rare, but they are able to drain regular enemies' health in groups.
A good boss slayer usually has one thing: a quick splash that has compressed, multihit segments. A fully leveled conventional splash attack has 6 segments, each doing one hit. Every 5 points in your magic stat increases the number of segments by 1, so by using Beholder and the Unicorn Horn, the player can increase their number of segments up to 8. Bosses and large enemies do not take knockback from splash attacks, so the priority of these splashes is to always land as many hits as possible on these enemies. If the segments are closer together, they are able to all collide with a target easier. Additionally, Fencer and Industrialist have 20% reduced base damage, but four hits per segment, which essentially triples their damage output.
Some characters have the ability to use their splash midair, which can be a safe option to take down crowds. The only difference between conventional magic jumps, projectiles, air projectiles, and Elemental Infusions are their elemental effects.
A few reasons for a character to be "bad" can be inferred from what makes them good. Low tier characters usually have weak knockback, low hits, and high delay. Characters with unconventional splash attacks are usually not preferred as they lack the usual safe options a normal splash offers, such as King or Bear.