Trials are challenges given to players in order to improve their understanding of a character's capabilities. A trial mode is available in the Street Fighter EX series (where it is called Expert Mode), the Street Fighter IV series, Street Fighter X Tekken, Street Fighter V, and Street Fighter III: Third Strike Online Edition.
Trials generally go over some of a character's available attacks and combos, and increase in difficulty as the player completes them.
Of note is that, in some cases, the trials do not necessarily have to be completed in the exact given order, although this is the 'default' method. The player can use certain moves to keep the dummy in a vulnerable state and give them the time needed to perform the next required move. A trial can be cleared so long as the player strings together a combo involving the listed moves, and they are used in the order given. Naturally, the dummy must not leave the hitstun state at any point. (e.g. they hit the floor, the player takes too long to string the hits together and the dummy recovers, etc.)
In all games, the mode functions similarly to Training Mode, where the player is provided with a character that serves as a training "dummy" for the player to practice combos on; as such, Trials are a more learning course organized method of training with pointers and guidelines to help build foundational form to grasp the intended characters selected. The dummy will take appropriate action based on the type of trial, e.g. jumping for anti-air combo trials, and using basic attacks for counter-based trials. As with Training Mode, KO is normally impossible for either character, except in Street Fighter IV Volt (where success KOs the opponent) and Street Fighter X Tekken (via Pandora; in this case, the scenario is simply reset). Trials, whether completed or not, may be returned to at anytime to revisit the lessons and challenges given.
The number of Trials and the training "dummy" provided vary with the game.
Trials by series
Street Fighter EX series
The PlayStation version of Street Fighter EX Plus α is the first game to feature trials. Each of the default characters has 16 trials of increasing difficulty, classified in ranks from E to A; by completing trials, the player can unlock the secret characters (Evil Ryu, Bloody Hokuto, Cycloid Beta and Cycloid Gamma), select the stronger CPU versions of M. Bison, Akuma and Garuda, and play the barrel Bonus Stage.
The Expert Mode in Street Fighter EX2 Plus is largely the same as before, though the secret characters do have trials in this game. Completing these trials unlocks Garuda, Kairi, Shadowgeist and Hayate, as well as the Bonus Stages and Maniac Mode (an additional, much more difficult trial mode for each character, which is classified as rank S).
Although Street Fighter EX3 does not have a standard Expert Mode for all characters, it does have the Ace Missions, where the player controls Ace and has to complete a series of challenges in order to unlock new moves for him.
Street Fighter IV series
In Street Fighter IV, each character has 24 trials. Trials are grouped into sets based on their difficulty: a first set of a 5, a second set of 7, a third set of 5, a fourth set of 4, a fifth set of 2, and the final 24th trial. There is a short break between each set.
The first half of these trials usually go over some of the character's basics, i.e. normal attacks, special attacks, Super Combos, and Ultra Combos. The 'intermediate' group of trials often task the player with chaining at least 2-3 moves together into a relatively simple combo, usually including one with a Focus Attack. The harder trials, all in the last half, involve slightly more complex moves, and often combo into that character's Super and/or Ultra Combos. The last few trials are the hardest, and often require the player to chain together normal moves, but with very strict timing.
In Super Street Fighter IV, the order of the trials is changed; the player can now retry, progress to the next trial, or quit to the trial menu after any trial is completed. The strict-timing combos are rearranged, now coming after the more basic trials. The latter half of the trials is harder as well, and may use Focus Cancels and other advanced techniques in combos that lead into a character's Super or Ultra Combo.
The trials were not changed for the Arcade Edition update; however, Ultra Street Fighter IV adds a separate Ultra Trial mode, which adds trials for the newly added characters in both games. The two modes are separate due to the changes in mechanics introduced in Ultra, especially the multiple changes in frame data (startup, cooldown, etc.) for each character and the Red Focus Attack, which (along with EX Red Focus Dash Cancels) is included in some of the new characters' later trials.
Of note is that a select few trials take advantage of the Training Mode-like conditions, and as such are not possible in normal gameplay, e.g. infinite Super Combo Gauge that allows for Super Combos to be followed with EX Specials, or multiple EX Red Focus Attacks and/or Dash Cancels.
Unlockables include character specific icons and titles for player vanities for offline and online play.
Street Fighter X Tekken
There are 20 trials for each characters, and they are designed in a way similar to Super Street Fighter IV.
In Street Fighter X Tekken, The Street Fighter cast have to complete their trials against Kazuya Mishima, while the Tekken cast have to do their trials against Ryu. There are no other differences aside from the character.
Street Fighter III: Third Strike Online Edition
Each character has 5 trials, composed entirely of multi-move combos. The "dummy" provided varies with the character and trial, as explained below.
Street Fighter V
In Street Fighter V, depending on which Volume, each character has 10 trials. The first half of these trials usually go over some of the character's basics,such as cancelling into a special attacks, or comboing off of a Counter-Hit. The second half usually consists of combos that require a V-Trigger activation. The final trial typically results with the combo ending with the character's Critical Art.
Similar to Super Street Fighter IV; the player can retry, progress to the next trial, or quit to the trial menu after any trial is completed. In addition, the player can choose whether the character's move names or input commands will be displayed. The player can also view any of the trial's demonstration to see what the actual combo looks like, before attempting.
Trails are divided up into Volumes. Each volume has a ten different combos for each character. There were a total of 2 volumes, until Street Fighter V: Arcade Edition, where a third Volume was added. In Volume 3, only the Season 3 characters have 10 trials while the original, Season 1, and Season 2 characters only have 4.
In Street Fighter EX Plus α, the training dummy is Evil Ryu in his red alternate color. In EX2 Plus, Ken is the dummy for the normal Expert Mode, and in Maniac Mode the dummy varies depending on the character. The Ace Missions in EX3 have Zako A as the dummy.
In the home console ports of the Street Fighter IV series, Dan (in training gear that serves as his first alternate costume) serves as the training dummy. In Street Fighter IV Volt, Ryu serves as the training dummy, and is the only one that can be KO'd, which is done by completing the trial. Both characters are set to take a hit and block as soon as they exit hitstun.
In Third Strike Online Edition, the dummy varies with the trial, as some of the combos may be character-specific (e.g. a combo that would only work on opponents the size of Hugo).
Street Fighter X Tekken uses Ryu as the default dummy for all Tekken character trials, and Kazuya for all Street Fighter character trials.
Street Fighter V uses Ryu as the default dummy for all characters.