Spell Cards (formerly known as Magic Cards until Magician's Force) 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 (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 are 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).
Some very powerful Spell Cards have been banned from tournament play, like "Raigeki". Konami 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, or "Flash of the Forbidden Spell" (whose card's title is indicative of a less-powerful replacement to "Raigeki"), which requires that all five of your opponent's monster card zones be filled with monsters in order to activate.
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.http://
A 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, however some media give them a capital N 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.