Blaze Accelerator can be used to destroy any of your opponent's monster and this effect can be used multiple times in one turn, a great card for controlling field advantage making it a key card in this deck. However, to use its effect, you need to discard a Pyro-type monster with 500 or less attack. Volcanic Shell is the perfect cost for Blaze Accelerator's effect, because after discarding him, by paying 500LP you can add another Volcanic Shell to your hand. Volcanic Rocket is used to add Blaze Accelerator to hand after he is normal summoned. Keep in mind that you cannot attack the turn you use Blaze Accelerator's effect.
Volcanic Shell is a really great card to discard because he replaces himself with another copy from your deck. This also means he can be used to thin down your deck helping u draw other useful cards. Many Counter Trap cards have powerful negation effects but require you to discard 1 card from your hand, but with Volcanic Shell this cost can be used to your advantage.
Summon Royal Firestorm Guards when you have 4 or more Pyro-type monsters in your graveyard, to activate his effect and draw 2 cards. Return as many copies of Volcanic Shell back into your deck to use them as costs for your effects later.