Frieza 6th Form is the 6th form of Frieza. He has a bulky build and is very strong.
Frieza was in Hell, trying to train, but Cooler kept interrupting him. So Frieza found a place no one knew about, and he trained there for 10 days. Those days made him so much stronger that he couldn't hold back his power in his 5th Form, so that power created his 6th Form. He easily surpassed Cooler and had the power of his father's Final Form.