Omni Lord of Friendship, Burn Nova/Rulings

Japanese FAQ Rulings (Source)

 * Q2461: If you have only this card in your hand, can you call it?
 * No, you cannot. In order to drop one or more cards from your hand, you need at least one card other than this card.


 * Q2463: If this card leaves the field during the turn that it entered the field, will you take damage after that?
 * Yes. "During the turn that this card entered the field" is the continuous abilities when this card is on the field. If it leaves the field, the effect will becomes invalid.