how can bewd's atk strength become 3000 from 3300 suddenly.
Because Lumis(or Umbra, I cant remember which) played some mask card on Blue Eyes to lower its attack points to 2300. Then he played mask of brutality on one of his monsters to raise its attack power by 1000. Then Yugi activated his fairy's refpanal to move the mask of brutality onto the Blue Eyes raising its attack power from 3000 to 3300. You must have been asleep during that part.
Actually, the BEWD's attack power was raised from 2300 to 3300, not from 3000.
the first person who wrote the goof was right after tygi uses the fairy's mirror to use mask of brutality on bewd its atk gets to 3300. But when Umbra or Lumis summons des guardias and is deciding who to atk , they show the bewd's atk as 3000 when it should be 3300. That is why only bewd gets destroyed when otherwise both the des guardias and the bewd should have got destroyed.
Blue-Eyes' attack power stayed at 3300, but it should have increased to 4000 because Mask Of Weakness works for only on turn.
Remember, Mask of Brutality was still Lumis' card, even though it was on the Blue Eyes. MoB has an Upkeep Cost, which was being absorbed by the Masked Doll. However, Lumis STILL decline to pay the cost (Even though it would've been 0) and destroy the Mask. Hence, by the time Lumis summoned his Guardius, the Mask was gone.