Chrono Trigger

In-game reset:
Hold L + R and press Select + Start.

Alternate endings:
A new option will appear after completing the game for the first time. Use this option and load a saved game to restart with items obtained in the previous game. Complete this special game to view an alternate ending sequence.

To see dialogue from Chrono himself, choose the new game plus feature after completing the game for the first time. Defeat Lavos after Schala opens the seal on the door leading to the throne room. Before you go through the door, return and defeat Lavos to see Chrono scold Marle and Lucca for admiring men instead of showing a slide show.
Information in this section was contributed by Cdderek.

There are about twenty different endings in the game.
Information in this section was contributed by Kevin Bender.

To see an alternate ending which features Frog marrying Queen Leene, complete the game. After just saving the Queen go to Lavos by any way you can. If you defeat Lavos a sequence with Leene marrying Glenn, and Marle being a toad princess will appear.
Information in this section was contributed by JINN.

Go to New Game+ and start with your best data and go to the fair. Then, go to Lucca's invention. Go to the pod to the right and you will fight Lavos alone as Chrono, but with all your stats and weapons from your old data. If you defeat him, you should see three people in a castle. After you talk to all three of them you should see what is the End of Time place with weird characters. However, these are the creators of the game in disguise. The time portals lead to more places with the staff.
Information in this section was contributed by HighFly2000.

Hidden ending:
There is a hidden ending that features a development room if you complete the game on your first attempt. You wll fight and defeat the Lavos Shell, Lavos, and Lavos Core, immediately after the queen calls Lavos into being in 12,000 BC. This would be the first attack on Lavos ever in the game. [Screenshot]
Information in this section was contributed by Anthony Cicatko.

Deleted saved games:
Enter the save game file selection screen. Highlight the saved game to delete then press Start + Select on controller two, then confirm your selection.

Hint: New Game+:
To get New Game+, you must complete the game by defeating Lavos through the Black Omen. After the game ends, reset to get the Game+ option to appear. When you choose "New Game+", you will be asked which save file you want to start with. Choose one of the three files and the game will start from the beginning. You will start the game at the same level, and with all of your spells and items that you had before. This option lets you play through to get each of the ten different endings. In a New Game+, a teleport (the Lavos Gate) directly to Lavos will appear in the right telepod of Lucca's invention at Leene Square. Depending upon when you enter this gate and defeat Lavos, you will get different endings
Information in this section was contributed by shaun witt.

Glitch: Save anywhere:
In Giants Claw or Tyrono Fortress there are a few switches. One activates a save point, one starts a battle, and one makes part of the floor disappear. First activate the save point, then make the floor disappear. Go to the top of the left hole, jump off and press A just as you go onto it. Save and continue. If done correctly, you should be able to save anywhere except in battles until the system is turned off.
Information in this section was contributed by BigBro9716.

Glitch: Packaging:
On the cartridge label, Marle is using Fire magic instead of Ice.
Information in this section was contributed by Liquid-zero5.

Glitch: Robo reappears:
There is an optional mission to revive the forest in 600 A.D. To do this you must leave Robo behind, go to the present time, and pick him up after his work is done. If you do not pick him up, he should be in Fiona's Shrine in the present forever. However as soon as you complete the game, he is there with you.
Information in this section was contributed by Jay.

Glitch: Computer reference:
In A.D. 2300, Lucca calls a device a computer. Because she is from 1000 A.D., there is no way she could know what a computer is.
Information in this section was contributed by Crimson Mantis.

Glitch: Ayla's name:
Have Ayla as the middle person in your party, and have her named anything other than Ayla. After Crono leaves the party, you must get the clone of Crono in order to bring him back. After going to Norstein Bekkler and doing the Mimic Game, return to Crono's house to get the doll from Crono's mother. Ayla will step up, and will say "Ayla need to borrow this" no matter what you named her (for example, "Kitty: Ayla need to borrow this!").
Information in this section was contributed by JR Van Esbroek.

Glitch: Invisible Lucca:
Due to a glitch with the walk through walls cheat, you can easily leave Lucca behind from the prison break. As you run through past the chancellor and down the stairs, exit as normal. However, when Marle joins you to leave notice that Lucca ran into the castle to save you, but eventually does not meet up with you. You can still continue as if she existed, but she may not return until the end even though she still talks.
Information in this section was contributed by Dracolix.