When Boil’s mana is filled, a dialog box shows up asking whether to cast it. However, even when “Confirm” is tapped, the spell does not cast. This might be caused by the opponent having no blue supports, but in that case the spell should either destroy all blue gems when “Confirm” is clicked or it should be grayed out like similar spells that can’t be cast for some reason.
//Edited Title - Tombstone