Warning: Sinner's are not creatable unless you are capable of playing as tier 1-5 with a different character. These beings who can escape hell are ment to be seriously powerful and because they start with 100% power unlocked This is for the sake of fairness as it took Mr. OP as fuck ichigo to take out the two best of them. ( nuff said :3 )
Now, by full power, we mean for that tier. A 2-3 Sinner is equal to a 2-3 shinigami in shikai. A 1-5 Sinner is equal to a 1-5 shinigami in bankai. A 1-1 Sinner is even to a 1-1 shinigami in toukai. Those are just examples, but it's the same with everyone else.
Sinner's powers are as diverse and unique to their owners as a Human's powers or even their fullbring! This makes them very good to make if you want a pure evil character that is LIKE a human but isn't a human. This is also a way to be evil without being forced to make a hollow or an arrancar.
However Sinner's get a huge racial boost. See below.
Enhanced Physical Capabilities They were shown to be able to fight physically against bankai using shinigami. For the purpose of Forum RP this would mean you get a boost to strength automatically for being a Sinner giving you x4 strength. This would be very useful when fighting people your tier since their bankai and shikai give them bonus's as well. The above covers the following list of physical attributes: Strength, Endurance, Stamina, Speed, Reflexes.
This may not seem like much.. But when you consider that they are supposed to be strong. This actually helps alot to counter bankai or shikai bonuses. Adding this to the unique powers you create for your character you could be among the strongest for your tier!
Also notable they have their own version of Shunpo called Ranzig. This is like shunpo in every way except it is for sinners.