The ability pixilate and refrigerate. Changes normal type move of ability bearer into fairy and ice type respectively. Does the Pokemon gain STAB from the move?
Gardevior is sent out. Mega evolves. Enemy use move on it. Mega Gardevoir uses hyper beam.
Does the move hyper beam gain STAB. If it does, hyper beam is 300 damage.
Aurorus is sent out. It uses a normal type move like take down or hyper beam. Does the normal type move gain STAB?
Pixelate and Refrigerate work in more or less the same way Normalise does. While Normalise changes all moves to Normal, Pixelate and Refrigerate change all normal moves to Fairy & Ice respectively.
Therefore, Pokemon like Pixelate Sylveon and Refrigerate Aurorus will always gain STAB from Normal moves, because they have been changed into Fairy and Ice.
If they didn't gain STAB, there would literally be no point to their abilities.
Does Normalise STAB the Normalised moves
Pixilate and Refrigerate also increase the damage by 30% so 150 x 30% = 45 + 150 = 195 before STAB, STAB = 195 x 50% = 97.5 + 195 = 292.5. That is the damage of Hyper Beam after Pixilate/Refrigerate and STAB, so like Flame-red said 300 damage it is pretty close to 300 but not exactly.