Forum:Grapha, Dragon Lord of Dark World HELP!

Can you use Grapha's Special summon ability during your opponents turn?

Also, Laval forest sprite got me thinking earlier, when it is sent to the grave all lavals gain atk of 200 X Number of 'Laval' monsters in grave until the end phase. If some of the laval monsters would leave the grave (i.e through lavalval dragons ability) would the atk of the lavals on the field go down?