These can apply to badfic of pretty much everything:

Dies, falls into the canon (usually a Stu, but I see it happen with Sues as well)

Suddenly, the team always had another member!

Suddenly, they're scouting out talent and this person is so awesome!

Suddenly, the canon characters are villains! (OC as the anti-hero fighting against them. This can be done very well, but is often... not.)

Constantly swearing, wears black and purple, much darker than the actual setting, possibly adds gore where there should be no gore.

The daughters and sons of the canons continue their adventures!

Way too smart for a teenager.

Kids joining adult teams.

Wears an improbably skimpy outfit, seduces canons.

Reads like a straw feminist caricature.

Kills a canon character.



This probably reads a bit more like a charge list than what you were looking for, but at least some of it should hopefully be useful.