Guys? This evil plan... sucks ass.
Susie, after Kris and Ralsei use a duck design for their Thrash Machine.
The Thrash Machine is a player-designed machine that makes several appearances.
In Chapter 1, Susie and Lancer "trick" Kris and Ralsei into designing a machine to "thrash [their] own ass." Lancer and Susie later build the machine poorly, but blow it up because it "sucks." In Chapter 2, Rouxls Kaard retrieved the machine from the King's trash, and brings it to Cyber World, where he repairs it and uses it on multiple occasions.
While walking in the Forest, Kris and Ralsei encounter Lancer, who claims to want to impress Susie by creating the perfect "Machine to Thrash Your own Ass." Kris and Ralsei agree to help design the machine.
The Thrash Machine has three different components: Head, Body, and Shoe. Each component has four different parts that the party can choose from, with the fourth option always being "Duck." Each part offers points in different styles from among "Elegant," "Lively," "Cute," "Hot," "Cool," and "Gun's". All parts provide one point in two different categories, except the "Duck" parts which provide no points in any category.
The available parts for each component are as follows:
- Laser: An enchanting gun with an air of mysticism. [+1 Cool and Gun's]
- Sword: A tomboyish blade reserved for upscale events. [+1 Elegant and Lively]
- Flame: It's burning with desire! Sure to make you blush! [+1 Cute and Hot]
- Duck: Garbage. You're going to lose points. [No Bonuses]
- Plain: Streamlined chassis for elegant thrashing. [+1 Elegant and Cute]
- Wheel: A fast chassis for tomboyish thrashing. [+1 Lively and Cool]
- Tank: Chassis for gun's lovers. The cannon is highly kissable. [+1 Hot and Gun's]
- Duck: Just looking at this is making you lose points. [No Bonuses]
- Sneak: Sporty shoes for the athletic thrashing machine in your life. [+1 Lively and Cute]
- A.Whl: Attractive wheels, leading the way! [+1 Hot and Cool]
- Tread: Weaponized treads for raiding sophisticated dinner parties. [+1 Elegant and Gun's]
- Duck: You're going to lose points. [No Bonuses]
After selecting a part, the party can also choose a color for that part, selecting the color using a slider on a color bar.
When completing the design, if "Duck" is chosen for all three components, the confirmation message mentions that their machine "sucks ass."
Once the machine is built, Lancer compliments Kris and Ralsei for their efforts, followed by Susie emerging from a bush to reveal it was all a plot to get them to design the machine that will thrash them. Susie then looks at the blueprint and has a unique reaction depending on the category that has the most points. As long as a full "Duck" design isn't created, Susie compliments Lancer for tricking the party into designing the machine.
- Heheh, it's even kinda high-class lookin'! [Elegant]
- Heheh, it even looks kinda fast. [Lively]
- Heheh, it almost looks kinda cute. [Cute]
- Susie: This thing's like... Ugh, hey, why did you draw something, like, ...it looks like you guys wanna kiss?
- Ralsei: (It's OK to express yourself, Kris.)
- Heheh, it even looks kinda cool. [Cool]
- Heheheheh...! ...uhh, didn't know you guys liked guns that much? [Gun's]
- Susie: Heheheheh...! ... ... It's just a duck? Guys? This evil plan... sucks ass.
- Lancer: Am I at fault in any way?
- Susie: Nah, you're good.
- Lancer: Oho! The bad guys get off scot-free again!! Thrash-you-later, you fools!!!
After traversing the Maze, Kris and Ralsei encounter the machine, only for it to be revealed that it is built out of junk (except "Duck" parts). Susie and Lancer appear and promptly blow the machine up, declaring the design sucked anyway, then engage Kris and Ralsei in a fight.
Rouxls Kaard retrieved the Thrash Machine from the King's scrap heap, and took it with him to the Cyber World, where he repaired it at the scrap shop. Due to his repairs, it looks like it did in the blueprint, rather than the poor quality replica that Lancer and Susie built. Rouxls consistently seems confused as to what the machine is.
In the Acid Lake in the Queen's Mansion, Rouxls Kaard confronts Kris and Ralsei atop the Thrash Machine, describing it as an "Effigie of an Ancient God of Combate." Usually, Ralsei recognizes the machine and tells Rouxls that it is their rejected design; however, if the machine is the Duck, Ralsei instead comments that it is just a duck.
Rouxls then battles the party. Some of the attacks that Rouxls uses are dependent on the parts used:
- Head attacks:
- Laser: Fires lasers which snake around the bullet board, similar to Werewerewire's.
- Sword: Fires spinning swords that boomerang back, similar to Susie's as a boss, albeit the swords having a smaller hitbox than Susie's axe.
- Flame: Spews fiery projectiles in a vertical sweeping motion.
- Duck: Fires a duck that travels in a horizontal line slowly. This attack deals 1 damage if it hits. Upon reaching the bullet board's left border or hitting the SOUL, it will fall off the board. It can be easily grazed to farm TP.
- The machine lunges into the bullet board. Depending on the machine's shoes part chosen, it has an additional attack:
- Sneak: Shoots star projectiles as the machine stomps, similar to K. Round.
- A.Whl: The machine lunges faster. Also shoots tire projectiles when the machine is on the left side of the board.
- Tread: Fires missiles upwards from the tread. The missiles fall back when the machine returns to its original position.
- Duck: The Thrash Machine charges across the board. If the whole machine is a duck, this attack explodes for 1 damage if it touches the SOUL. Otherwise it continues moving for moderate damage.
After the battle, when Rouxls turns to stone and lands on the houses, the ensuing explosion launches the Thrash Machine off-screen, where it presumably sinks into the battery acid.
When GIGA Queen knocks the party off the top of her Mansion, Berdly arrives with a number of allies to help the party. Among these allies, recruited enemies from Cyber World, the Hacker (if the blue checkmarks were collected), and Starwalker (if interacted with in Chapter 1) all combine their powers to help the party, followed by Rouxls Kaard adding the Thrash Machine. These all combine into a giant mecha of similar size to GIGA Queen, that is also named "Thrash Machine".
The Thrash Machine mecha has the head of the original Thrash Machine, but a completely different body. Its body seems to borrow design elements from each of the party members. It features elements of Kris's scarf and chestplate, Susie's spiked bands and Ralsei's cloak. In the ensuing battle with GIGA Queen, one of the Thrash Machine's ACTs is determined by the Thrash Machine's head.
After the battle, Queen destroys the Thrash Machine mecha by punching it in two with GIGA Queen's detachable fist.
The Thrash Machine's HP is dependent on the number of enemies recruited, and whether the Hacker and Starwalker contributed to its assembly. From a base of 200 HP, each recruit (including Hacker and Starwalker) provides 5 HP, up to a maximum of 250 HP. Recruiting all enemies will yield the maximum HP, even if the Hacker and Starwalker did not contribute.
The Thrash Machine's attack power is based on Kris's Attack stat. Its defense is independent, however.
Like Kris, the Thrash Machine has an ACT menu instead of a Magic menu.
- [Head]Mode: 50 TP (name and effect depend on the head chosen for the Thrash Machine in Chapter 1)
- LaserMode (Laser head): "Fast Attacks" (Increases damage somewhat and allows for faster punches for a turn afterwards)
- SwordMode (Sword head): "Power up each hit" (Increases damage moderately and makes each successive hit stronger, until the next miss.)
- FireMode (Flame head): "Power Attacks" (Increases damage from attacks afterwards (with about 420 initial damage on Phase 1).)
- DuckMode (Duck head): "Sucky Attacks" (Gives duck orbitals that heal the machine by 2 HP per hit, or 4 HP for hitting back the final attack. Duck Aura also heals 35 HP upon initial hit but does not deal as much damage (about 150 Phase 3).)
- SELF-FIX: 20 TP (Heals 100 HP, but its cost increases by 10 TP each time it is used, up to a maximum 50 TP cost)
- Turbo Dodge: 25 TP (Increased dodge length and speed)
- During Undertale's 6th anniversary stream, Toby Fox stated there was no Thrash Machine battle during Chapter 1 because it was "too much effort."
- If a Chapter 2 file is started from scratch (without a finished Chapter 1 file), the Machine has a random construction. This can be manipulated with certain actions in the load menu.
- The Thrash Machine may have some form of sentience, as during the Rouxls Kaard house battle it is stated to "reluctantly fight you." If the machine is a duck, it is also stated to have "fallen in love" with the party's swan boat.
- It shares the same healing amounts from Choco Diamond and Hearts Donut with Kris.
- Queen's line before her final attack refers to its original purpose: thrashing the party. However, it is unclear how she knows this, as its purpose was only stated in Chapter 1.