OCG Rulings

• Special Summoning this card from the hand is an Ignition Effect that activates in the hand.^[1]

• Discarding 2 WATER monsters to the Graveyard is a cost.^[1]

• The effect that adds 1 "Abyss-" Spell or Trap Card to the hand does not target.^[1]

• Tributing 1 other face-up Attack Position WATER monster you control is a cost to activate the effect that allows this monster to attack twice during the same Battle Phase.^[1]

• The effect that allows this monster to attack twice during the same Battle Phase is an Ignition Effect that you can activate during your Main Phase 1.^[1]

• If "Mind Crush" is chained to the activation of the effect of "Mermail Abyssmegalo", so that it is discarded from the hand, since "Mermail Abyssmegalo" itself is no longer in the hand, it is not Special Summoned.^[2]

• If when the effect of "Mermail Abyssmegalo" or "High Priestess of Prophecy" that Special Summons itself from the hand is activated, "Call Of The Haunted" is Chained targeting "Jowgen the Spiritualist", since "Mermail Abyssmegalo" or "High Priestess of Prophecy" cannot be Special Summoned, it remains in the hand.^[3]

References

1. ↑ ^{1.0 1.1 1.2 1.3 1.4} Konami OCG Card Database: Mermail - Megaloabyss
2. ↑ Konami OCG Card Database: If "Mind Crush" is chained to the activation of the effect of "Mermail Abyssmegalo", so that it is discarded from the hand, is it still Special Summoned?
3. ↑ Konami OCG Card Database: When the effect of "Mermail Abyssmegalo" or "High Priestess of Prophecy" that Special Summons itself from the hand is activated, "Call Of The Haunted" is Chained targeting "Jowgen the Spiritualist", how does the effect of "Mermail Abyssmegalo" resolve?