SS: These are gods that are simply overpowered and beat everything if played correctly. If you aren't playing an SS god you should ALWAYS ban it. (Hou Yi is a placeholder, the list keeps automatically putting his picture there)
S+: These are gods that are nearly overpowered and quite strong. They beat most gods in the game but can be outmatched by other S or S+ gods. These are top ban material.
S: These gods are basically the same as S+ but are slightly weaker. These are still top bans.
S-: This is for gods that are strong but can be easily beaten by S tier and above if played correctly. These can be ignored in the banning phase for the most part since S and above is so strong.
A+: These gods are just above the point of being balanced and have good strengths but can be defeated by the S level gods and can hold their own against most other gods.
A: Gods in A tier are balanced and are not too strong or weak. They aren't the best picks but should always be considered based on bans and player skill with the gods. Gods in A can beat higher tiers in the hands of skilled players.
A-: These gods are slightly under performing but are by no means bad picks. Skilled players can consider these picks despite their weaknesses.
B: This tier is for those gods that do well in very specific matchups and situations but most of the time under perform. These are not recommended unless you are an expert with these gods.
C: These picks are generally considered bad because they are either too vulnerable or cannot deal damage efficiently. These should be considered by experts only, but it is highly discouraged even in this case.
D: These are the worst picks in Duel and should never be considered in any circumstances.