There are so many great Spell Cards out there that if this was a Top 10 list, cards 10 through 6 could be slotted anywhere in their rankings. But since this is a Top 5 list, it means that these 5 are mandatory in any dueling deck to ensure victory. For this list I do not consider if it is unlimited, limited, or forbidden in the Advanced or Traditional Formats. It is simply based on importance in a duel.
Honorable Mention - Book Of Moon, Burial From A Different Dimension, Polymerization, Mystical Space Typhoon, Lightning Vortex, and Smashing Ground.
5. Heavy Storm
Destroy all Spell and Trap Cards on the field.
The difficult part of dealing with Spell and Trap cards in a duel is that you don't know what they are until they are activated (because they are placed face down on the field). By then it's usually too late to do anything about and your opponent has you in a world of hurt. The solution? Destroy them all before they can hurt you. Just make sure you don't have any Spell or Trap cards of your own that might get caught up in this tornado.
4. Dark Hole
Destroys all monsters on the field.
This is your last line of defense when an opponent brings out a Monster that you can't handle. Unlike Heavy Storm which you should activate when you're up against more than a few Spell and Trap cards, Dark Hole needs to be utilized a bit more carefully. You don't want to waste this card just on any simple monster. If you don't have a monster in play to stop an opposing monster (especially one that is an absolute beat stick), activate this card and wipe them all out. It's basically a monster reset button when you are desperate.
3. Pot Of Greed
Draw 2 cards from your Deck.
Two words...card advantage. If you think about it, normally it would take two rounds to draw two cards (one card per round). With this card you don't need to wait. The simple fact that you can get cards in your hand faster means you have the advantage over any opponent. The key to winning a duel is getting your monsters on the playing field quicker than your opponent. No other card does it better.
Destroy all monsters on your opponent's side of the field.
Unlike Dark Hole, this card only destroys your opponent's monsters. How important is that little difference? Dark Hole puts both you and your opponent back to even whereas Raigeki gives you an advantage. Once the field is clear and you have a huge ATK monster in play, the monster is going directly for your opponent's life points. Game changer. Game ender.
1. Monster Reborn
Special Summon 1 monster from either player's Graveyard to your side of the field.
Was there ever any doubt that this card would be #1? If there was it means you haven't been dueling for very long. Monster Reborn lets you revive not only your strongest monsters, but also lets you steal an opponent's monster from the Graveyard if you choose to. Part of the Yugioh dueling world since it began, this card has been a staple in every dueling deck. From the novice to the tournament champions, Monster Reborn is the apex Spell Card in their deck.