The text stating that this card must be Special Summoned by Fusion Summon is not an effect.[1]
Even if this card was previously Fusion Summoned, it cannot be Special Summoned from the GY with the effect of "Monster Reborn", etc.[1]
This card's effect that increases its ATK is a Continuous Effect.[1]
This card's effect that Special Summons an "Elemental HERO" Fusion Monster from your Extra Deck is a Trigger Effect. (It does not target. Tributing this card is the cost to activate this effect.)[1]
This effect can be activated optionally at the end of the Damage Step when this card destroys an opponent's monster by battle.[1]