The Dragon’s Lair

This is what you’d been waiting for. You stand outside the magnificent, gigantic opening to the Dragon’s Lair, where many had failed to slay a dragon, and get the gold from a nearby chest that the dragon protects with his life. Every living soul that entered the cave never exited. You are determined to change this fate. Pride in yourself, you storm into the endless-seeming cave. You see bones surrounding you as you pass through the dusty entrance. You walk further until your legs ache and you feel very dehydrated. But you’ve made it. You’d come to the end of the long trail, and are greeted by a massive, unrealistically looking beast sleeping in its natural habitat. You see your goal of the day, the chest of gold, clutched in this bigger-than-a-human claws. You think to yourself the amounts of damage that could possibly be dealt by something as sharp of this dragon’s claws. You start to look around to figure out a way to obtain the gold within the chest. You are in a dome-shaped room, lined with boulders of great sizes. You see a paper on the ground. You pick it up. On the paper it reads “USE THE MAGIC WAND TO YOUR RIGHT TO DEFEAT THE DRAGON. THERE ARE ONLY SIX DIFFERENT THINGS THAT THE WAND CAN DO, ACCORDING TO THE BOOK ON YOUR LEFT. THE SPELLS THAT YOU CAN CAST ARE WRITTEN IN THE BOOK PROVIDED. GOOD LUCK.” Almost as if they were untouched beforehand, there is a wand to your exact right, and a book on the opposite side. You look at the book. In order, you have the list of spells you could cast to defeat the dragon. The book says that only one will work, and the five others will end in your defeat. The spells are:

Power (Left) Spell (Right)

Fireball Fireballus
Shield Shieldus
Rocks Rock-Throwus
Armor Protectivus
Explosion Explo
Firework Fireworkus

What spell do you cast?