EXPLANATION TIME! Gagaga Girl, not shown, has the ability that when you summon an xyz monster (what machu mech is) can reduce the attack of a special summoned monster on your opponent's field. Gagaga sister's effect can combine its level (2) with that of another gagaga monster, namely girl (level 3), to both become level 5 so you rank 5 xyz summon. machu mech has the power to target a monster that has a different attack then their original attack and deal damage equal to that difference as well as gaining attack equal that that difference.
to non-yugioh players, gagaga sister, when played together with gagaga girl and machu mech, can give you the chance of winning without doing much else.
