Code Name: S.T.E.A.M. is a turn-based strategy game controlled in the style of a third-person shooter, similar to Sega's Valkyria Chronicles series.[5][6][7] The gameplay involves a team of characters controlled by the player known as the "Agents of S.T.E.A.M." facing off against an opposing team of alien invaders. For the player, both movement and attacking requires the use of "steam", a resource that depletes whenever a character moves around or uses their weapon, in the latter case depending on the type of weapon be used. By saving up the same amount of steam required for the character's weapon to be used, certain characters can perform "overwatch attacks" during the opponent's turn, letting them attack enemies that wander into their line of sight with the added potential to stun them for the rest of the turn. However, the opposing alien team can also perform this strategy, so caution is encouraged. Before each level, the player selects up to four characters, with more becoming available as the story progresses. Each character has their own unique primary weapon that suit different play styles and strategies and a secondary sub-weapon that can be swapped between characters before each level. Every character also has a unique innate ability that remains active even during the enemy's turn, such as moving around crates, passively buffing nearby allies, or surviving potentially lethal blows. Finally, each character has a unique special move that can be used once per level and does not cost any steam. These special moves range from area-of-effect attacks to temporarily buffing or healing party members.
The main campaign is divided into chapters which are subdivided into levels, with mission objectives such as reaching the goal, saving a number of civilians, or escorting a character to safety. Throughout each level, the player can collect gears and medals scattered across the map. Gears are rarer and hidden in each level, while medals are scattered throughout and can also be earned by defeating enemies, more if they are defeated with overwatch attacks. In between levels, gears are used to unlock "boilers" that can alter characters' stats and the amount of steam available, while medals are used to unlock further sub-weapons and can be used at checkpoints mid-match to save the game, heal themselves, or restore fallen allies.[8] Twelve playable characters are unlocked over the course of the story, but if the player manages to collect a grand total of 100,000 medals during gameplay, a thirteenth character is unlocked: a smaller version of the A.B.E. mech called "Stovepipe" (named after Lincoln's hat). Upon clearing a chapter in the campaign for the first time, that chapter can be revisited in harder challenge missions, such as by making steam and enemy health bars invisible or removing backtracking. Completing the chapter under these stipulations rewards the player with a medal bonus.[9]
Beyond the main campaign, Code Name: S.T.E.A.M. includes local and online multiplayer with three different gameplay modes. The first is a simple deathmatch mode where two players face off with their squads of four, with the added element of a 60-second turn timer. The second is "Medal Battle", which tasks the player to collect more medals than their opponent in only 5 turns. A small medal bonus can also be earned for taking out enemy soldiers. The third is "A.B.E. Battle", which pits two players against each other in giant A.B.E. mechs in real-time combat. Matchmaking online can be done either with random people or in tournaments, and medals earned in online matches can be transferred to the main campaign.[10] The game is also compatible with Amiibo figures, allowing players to play as Marth (voiced by Yuri Lowenthal), Ike (voiced by Jason Adkins), Robin (voiced by David Vincent), and Lucina (voiced by Laura Bailey) from the Fire Emblem series by scanning their corresponding figures.[11] Unlike the other S.T.E.A.M. members, the Fire Emblem characters cannot be revived at checkpoints should they fall in battle, and they must be revived by scanning their respective Amiibo figures again. Additionally, the Fire Emblem characters are not involved in the main storyline, and their equipment cannot be removed or swapped out.[12]
