“Berserk Dragon” cannot be Normal Summoned or Set, and cannot be Special Summoned EXCEPT by the effect of “A Deal with Dark Ruler”. So “Berserk Dragon” cannot be Special Summoned with “Monster Reborn”, etc., even if Special Summoned properly first.
If “Berserk Dragon” is removed from play with “Interdimensional Matter Transporter”, you cannot try to resolve “Berserk Dragon”’s effect before it returns to play; you must return it to play first and then it loses 500 ATK.
While “Skill Drain” is active, “Berserk Dragon”’s effects are negated. But “Berserk Dragon”’s effect doesn’t count turns, so if “Skill Drain” was active for 4 turns, and is then destroyed, do not reduce “Berserk Dragon”’s ATK for those 4 turns.
Netrep Rulings:
If “Berserk Dragon” is flipped face down, when it is turned face up again, it will have its original ATK value of 3500.
If “Berserk Dragon” temporarily leaves the field, when it returns, it will have its original ATK value of 3500.
If “Berserk Dragon” attacks Life Points directly, it may not attack any monsters that may later be on the field.