SpellTech Decks involve burning your opponents to 0 using the Tempest Magician, Citadel of Endymion, and the Tower of Babel very quickly while utilizing the Reactors, thus putting the enemy in some lockdown. The reactors also help to destroy potential threats and minimize spell counters needed for the assault to work. Thje key to this deck is to bring out Tempest magician and minimize the amount of spell counters needed for the combo th work. All the Exemplars serve to do just that - build up spell counters quickly, and swarm the field with spellcasters. Tower of Babel helps to gain 4 more spell counters and minimize the amount of spell counters by SIX, and gives four more spell counters to use. (babel takes away 3000 life points, each spell counter tempest uses eliminates 500 life points). Obelisk the Legal Tormentor serves to open doors for direct attacks, also reducing the spell counters you need greatly.
From the start of the game, you need 16 spell counters to work. The amount decreases every time your opponent takes 500 life points damage or more.
These cards are mandatory for a SpellTech deck to be called a SpellTech deck. Any other cards may help greatly.
Other Helpful Cards
Arcanite Magician/Assault Mode can be a handy replacement for Obelisk of you don't want to go through the trouble of getting 3 fodder monsters for Obelisk, and you can bring Arcanite back after it's gone.
Magical Blast can be good for burning the opponents life points, and can be reused. This helps for lowering the amount of spell counters needed for an OTK.
Blackwing - Gale the Whirlwind is a great Blackwing tuner that can be useful with Bora the Spear. Being level 3 tuner can be a great help.
DNA Surgery can turn all monsters into the Spellcaster-Type, which is helpful with Synchro Summons.
Frequency Magician is a tuner who ups the attack of another monster by 500 by giving up its spell counter, nice for direct attacks.
Speaking of direct attacks, Earthbound Immortals can work well with this deck, since you should always have a field in play. Earthbound Immortals can also srtike the opponent directly, which works well with this type of burner deck.
Flying Fortress SKY FIRE is an awesome reactor card, as long as you can spare some extra reactors. It can obliterate face-up and face-down cards and inflict huge amounts of burning damage, especially useful with multiple reactors, could form a greater lockdown deck.
While on the topic of lockdown, Ojama monsters have a lot of potential in this deck for a lockdown SpellTech deck. When Ojama Knight and Ojama King are on the field with the reactors or SKY FIRE, the opponent will be left with very few options. It can also be used in conjunction with the DNA Surgery and Magical Blast to whittle your poor opponents life points away.
Counters to this type of Deck
Exodia Decks can be a pain, since so little is required to summon all the pieces of Exodia quickly, and this deck cannot gather the needed spell counters in time.