If the number of “Skull Servant” and “King of the Skull Servants” cards in your Graveyard changes, re-calculate the original ATK of “King of the Skull Servants”. If it is equipped with "Megamorph" you would then re-apply the effect of "Megamorph".
If you have 2 "Skull Servant" cards in your Graveyard (original ATK 2000), and you equip this card with "Megamorph", its current ATK will become either 4000 or 1000, depending on your Life Points.
Since the ATK of this card is ?, it cannot be Special Summoned by the effect of "Mystic Tomato".
Removing from play 1 “Skull Servant” or “King of the Skull Servants” to Special Summon a “King of the Skull Servants” is a cost.