| Melkiador |
"Tiny creatures can occupy a space occupied by a larger creature as well, and, if their reach is 0 feet, they must do so in order to attack.", page 313.
"Tiny creatures are an exception. They can move through any creatures’ spaces and can even end their movement there. See page 313 for more on Tiny creatures.", page 312.
It's unclear if they still require an athletics check to tumble into the square, but they probably do. A lack of stats on the attack is the bigger problem. I'm not sure if these are just missing from the playtest bestiary, or if there are really no stats for them.