If a Level 6 or higher monster is Special Summoned and then its Level is decreased to 5 or lower, then the monster is unaffected by "Grave of the Super Ancient Organism". The monster can activate its effect and can attack.[2]
The effect of "Grave of the Super Ancient Organism" prevents the activation of effects; it does not negate effects once they are activated. If a Level 6 or higher monster which was Special Summoned activates an effect and "Grave of the Super Ancient Organism" is chained, the effect of the monster will not be negated. However, the monster cannot activate its effect again after the current Chain resolves.[4]
If a Level 6 or higher monster is flipped face-down and then Flip Summoned, or if a Level 6 or higher monster is removed from play temporarily by an effect like "Interdimensional Matter Transporter", then the monster is still considered to have been Special Summoned. Thus, it will be affected by "Grave of the Super Ancient Organism", so it can neither activate its effects nor attack.[6]
↑Konami FAQ: Will "Grave of the Super Ancient Organism" also negate the effect of a monster whose Level was decreased to 5 or lower after it was Special Summoned?
↑Konami FAQ: If "Chimeratech Overdragon" is Fusion Summoned after "Grave of the Super Ancient Organism" was activated, does its effect activate?
↑Konami FAQ: When "Grave of the Super Ancient Organism" is activated in chain to the activation of a monster's effect, is the effect negated?
↑Konami FAQ: Are monsters which were Special Summoned before the effect of "Grave of the Super Ancient Organism" was applied unable to attack?
↑Konami FAQ: Will the effect of "Grave of the Super Ancient Organism" prevent a monster which was Special Summoned from declaring an attack if the monster is flipped face-down?