Spell Cards

Spell Cards (formerly known as Magic Cards) are green-colored cards that have various effects to alter the play of the game. Often, a Spell Card has a single effect to provide a bonus to the user or a weakness to the opponent. All Spells are Spell Speed 1, with the exception of Quick-Play Spells, which are Spell Speed 2. You may play as many Spell Cards as you would like per turn. 
Although Spell Cards are often not as powerful as a Trap Card, they have the advantage that they may be played the turn they're drawn without having to Set them first. A Set Spell Card may be activated the turn it is Set as well (with the exception of Quick-Play Spell Cards). 
In a typical Deck, Spell Cards occupy a little less than half of the total deck size (around 12-15 cards) and collectively with Trap Cards often have a 1:1 ratio to Monster Cards. 
Some very powerful Spell Cards have been banned from tournament play, like "Raigeki". Upper Deck has released new, less-powerful replacements for some of these cards. For instance, "Raigeki" has been replaced in Advanced Format by "Lightning Vortex", which requires a discard and only destroys face-up monsters. 
Used properly, a single Spell Card can significantly alter the game in the user's favour.It isn't uncommon for a player to win a Duel with the use of a single Spell Card. "Snatch Steal" is a common example of a Spell Card that is capable of winning a Duel (though it has since been Forbidden). 
Types EditA Spell Card's type is designated by a symbol to the right of the words "Spell Card". The various Spell Card Types are: 
Normal Spell; No Symbol 
Continuous Spell, symbolized with an "infinity" symbol. 
Equip Spell, symbolized with a "plus" symbol. 
Quick-Play Spell, symbolized with a lightning bolt. 
Field Spell, symbolized with a compass. 
Ritual Spell, symbolized with a torch.