See "Gladiator Beast Alexander" for additional rulings.
If “Gladiator Beast Dimacari” is Special Summoned by the effect of a “Gladiator Beast” monster, it can attack twice during the Battle Phase. If “Skill Drain” is later activated, this effect is negated and “Gladiator Beast Dimacari’” will no longer be able to attack twice with its effect. Even if “Skill Drain” is later negated or removed from the field, “Gladiator Beast Dimacari’s” effect to attack twice during the Battle Phase will not be reapplied.
If “Gladiator Beast Dimacari” is Special Summoned by the effect of a “Gladiator Beast” monster and it is flipped face-down, when it is flipped face-up its effect to attack twice during the Battle Phase will not be applied.