After reaching 3 debuffs, both Players and Parties cannot gain additional debuffs until at least one of their current debuffs expires. (The Seven)

Unless otherwise stated, debuffs cannot stack with themselves, with repeated applications upon the same target simply causing the debuff duration to reset and not incurring increased effectiveness. All debuffs are either temporary or conditional and do not persist after the affected target's death. (League of Legends Wiki)

Blue Ban is a tad weaker than his counterparts, and is more a debuffer than an actual fighter. His Critical Pierce skill is very strong, especially against tanks, but that’s pretty much all he offers aside from his passive debuff, which can be easily countered. (BlueStacks)