Sending 1 Pyro-Type monster with 500 or less ATK to the Graveyard is part of this card’s effect. It is not a cost.
You cannot activate the effect of this card in the same Chain as this card’s activation. You can only activate the effect after this card’s activation is resolved, and it is face-up on the field.
If you activate this card's effect then you, the player, cannot declare an attack so even a monster unaffected by the effects of Spell Cards like "Horus the Black Flame Dragon LV6" cannot attack.