Sentence: Battle Preparations
■ [Set] ■ Abilities of all «Astrodragon» on your field cannot be nullified by your opponent's card effects. ■ When an «Astrodragon» monster enters your field, you gain 1 life and draw a card. This ability only activates once per turn. ■ You may only [Set] one "Sentence: Battle Preparations" on your field.
It's not that hard when you know what's coming.