Forum:Ultimate Offering

Can i use Ultimate Offering like this? -I summon Obsidian Dragon ATK Positon. -I pay 500 life points for 'Ultimate offering' and summon 'Poison mummy'. (May I activate it 2 Times per Turn?) -I pay 500 Life points and summon 'Neo-Space Dark Panther'. (Here is my question:) Can I pay 500 Life points and activate Ultimate Offering to summon a high lvl Monster(Light- and Darknessdragon)if i sacrify Dark Panther and Poison mummy? Or can i just summon 1-4*Monsters with Ultimate Offering?