Chrono Trigger/Techniques

Characters and Single Techs
Techniques within the game are made available as characters obtain tech points, which are obtained by having the given character fight in combat.

Crono
Element: lightning. Cyclone is a useful tech for taking out groups of enemies early in the game, although it's even better when combined with some of the double techs you'll have. Life is particularly handy since Crono is a fixture in your party, and just keep in mind what your best physical attack or magic spell currently is. Luminaire is the most powerful Single tech in the game under normal circumstances.

Lucca
Element: fire. You'll mostly just want to use the best fire spell Lucca has available. Does not have much overall variation besides fire-based attacks, but her high magic attack rating can dispatch a lot of monsters in very few shots. Protect can be essential when physical damage nearly exceeds the Maximum HP, such as Grand Stone (Lavos Final Form). Flare is the second strongest single spell in the game, below Luminaire.

Marle
Element: water. Marle uses water magic in the form of ice. As you can see she's almost entirely support spells. Haste is an extremely useful tech against long, drawn-out bosses like the Black Tyrano. and Life 2 is the best revival method in the game. Her drawback is the lack of healing spells that affect the whole party, but she does get a lot of Double Techs that compensate for that. However at later levels Ayla's Kiss will heal a party member for full health and consuming 1 MP, rendering most of Marle's moves useless as Ayla's techniques are stronger overall.

Frog
Element: water. Frog is required for the whole sequence in Magus's castle, and he has a good physical attack otherwise. The Heal spell is very useful, and Frog Squash is a killer, doing extreme amounts of damage when his HP is low (the best time to use this is just after he is revived). If you match him up with Ayla, you can use their first dual tech for the most MP efficient healing technique in the game: Slurp Kiss (heals the entire party for 1 MP from both characters).

Robo
Element: none. Robo is very slow, so he needs a lot of Speed uppers before he can unleash his full potential. He learns a damage-all tech early, which is useful during the Factory section where he must be in the party. His Heal Beam is also useful, but is weak in comparison to the other healing techs available to other characters.

Robo cannot learn magic, which is why he has no element, but can deal different types of elemental damage (except for water) with his techs, making him somewhat as versatile as Magus.

Ayla
Element: none. In general you'll probably be best off using the most powerful physical tech she has, and charm can be very useful for getting rare items. Dino Tail functions much like Frog Squash. If you match her up with Frog, you can use their first dual tech for the most MP efficient healing technique in the game: Slurp Kiss (heals the entire party for 1 MP from both characters).

Ayla uses entirely physical attacks since she predates the existence of magic on the planet. This makes her very ineffective against enemies with high physical defense.

Magus
Element: shadow. Although his specialty is Shadow, Magus has every kind of magic available to him and a strong physical attack, making him the most versatile character in the game when dealing with magic damage. Dark Bomb and Dark Mist do the same damage and Dark Matter, while powerful, isn't as strong as Flare and Luminaire.

One interesting note about Magus is that his versions of Lightning 2, Fire 2, and Ice 2 are about 30% more powerful than those cast by Crono, Lucca, or Marle, which makes him effectively the best Water magic user in the game among other things.

Double Techs
Every set of two characters, excluding Magus, has three double techs between them.

Triple Techs
One rule of thumb is that for every three character combination that includes Crono and doesn't include Magus has a triple tech. Thus, Crono Marle Frog have one, Crono Marle Lucca also have one, etc. In addition to these triple techs however, there are some hidden ones that can only be activated by finding a hidden "rock" accessory somewhere in the game and equipping it on one of the characters involved in the triple tech. To use any of these special triple techs you'll need to wait until The Time Egg when you're finally able to choose your party without Crono.

Note that tech required Triple Techs are unlocked by having all three party members in the party with each individual tech available for use. After a single battle with the party in that formation, the Triple Tech will be unlocked.

Tech Required
These triple techs require that all of the characters involved be alive at the time its use. To unlock a triple tech, the characters must have the required techniques unlocked, and must fight at least one battle together.

Accessory Required
These triple techs require one of the characters who are able to perform the triple tech (listed in the table) to wear a specific accessory that unlocks the technique for use. These are only available while the accessory is equipped.