Tiny Creatures and Flanking

Parent page Flanking

Tiny creatures usually have reach of 0 feet and need to be in a creature's space to attack it. This makes a Tiny creature unable to flank unless it's able to use a weapon with reach or has a melee unarmed attack with reach greater than 0 feet.

The GM might allow Tiny creatures to flank other Tiny creatures if they're all in the same square, but this is best left for special circumstances and uses the GM's best judgment.