Activate only during your opponent's Main Phase. After activation, Special Summon this card; it is treated as an Effect Monster Card (Machine-Type/EARTH/Level 4/ATK ?/DEF ?). (This card is still treated as a Trap Card.) If this card is selected as an attack target, the ATK and DEF of this card become the ATK and DEF of the attacking monster. This card is Set in its Spell & Trap Card Zone during your opponent's End Phase.
So if you have a field spell, lets say Gaia Power, will it still have +500 attack when it's being attacked or will the attack of this card become the same exact attack as a monster attacking this card without the field spell effect?