During the events of Arcs 1 through 4, Puck played a pivotal role for Emilia's mental state, supporting her and acting as her parental figure. During the events of the 4th Arc, however, Puck forcefully severed the contract with her in order to remove the seal placed over Emilia's memories, giving her a fighting chance in the Witch of Greed's Trials. After using every last bit of power he was capable of mustering up at that time, Puck entered a long period of sleep, inside a powerful Pyroxene Crystal which is currently worn by Emilia, however, the crystal isn't powerful enough to allow him to materialize.
In his smaller form, Puck stands at nine centimetres tall and is small enough to fit in the palm of a person's hand. Aside from his diminutive stature and the fact that he usually stands on his hindlegs, Puck is fairly physically reminiscent of a common house cat, specifically an American Shorthair. The light grey and white fur that coats his entire body is well-groomed and very soft. His eyes are icy green and his pink nose is another trait that separates him from a house cat. Puck's tail is abnormally long to the point that it is the length of his body and his ears are floppy yet extremely soft to the touch. On his left ear, Puck wears a single golden hoop earring that makes his ear droop down. He can also occasionally be seen carrying around a miniaturized magenta handbag that fits his small size perfectly.
Puck is generally a nice spirit. He is usually in a very good and happy mood, and usually stood at Emilia's side to protect her, affectionately calling her "Lia" or "my daughter". He occasionally shows his goofy side as well, which can be clearly observed during the events of the 2nd Arc, where Puck nonchalantly teases both Subaru and Emilia with seemingly no end. Furthermore, Puck gets along especially well with Beatrice. However, Puck's demeanour greatly changed in loops where Emilia died. When such tragedy struck, he was willing to destroy the world to save Emilia and to fulfil his vows with the Witch of Greed.
Despite his seemingly never-ending happy-go-lucky attitude, Puck usually reacts and acts very cold and sometimes even hostile with everyone else besides Emilia, Beatrice, Roswaal, Rem, Ram and Subaru. During the Royal Selection Ceremony at the start of Arc 3, Puck was mere seconds away from freezing the entire Royal Throne Room, killing everyone inside it–though it was revealed soon after, that the entire exchange was a plan devised by Roswaal, in order to have Emilia make a memorable impression on the Sage Council and the other four Royal Selection Candidates.
Around 400 years ago, Puck was a humanoid being but was created into an Artificial Spirit by Echidna to watch over Emilia. Roughly three years after his creation, he and Beatrice helped Tosca in fending off the Silver Dragons led by Falgal.
He had apparently left Echidna by the time she moved into the Sanctuary to look for Emilia. Seven years before the start of the election, Puck unfroze Emilia and began to act as her friend and mentor, and later on, started to live at Roswaal's mansion where he was reunited with Beatrice.
Artificial Spirit: Puck is a Great Spirit presiding over Fire Mana. While he was contracted with Emilia, he used to have a number of conditions, one of which was that he would only appear from nine in the morning to five in the afternoon, though he could use her Od to manifest himself in an emergency. Like Beatrice, Puck is also an Artificial Spirit, making him have a terrible mana consumption rate. He used to drain mana from Emilia, who didn't have any use for it until she remembered that she could use magic on her own during the trials, while lying that he was absorbing it from the atmosphere. Puck had a vow with Echidna that forbade him from forming a contract with Emilia on his own, however he broke this vow as he was on the verge of death, both as a means to save himself and to protect her from the effects of his battle with Melakuera. This resulted in his memories of the past being sealed.
Magic User (魔法使い Maho Tsukai):
Puck is very skilled at different types of Magic, such as Fire, Water, and Yin magic as well as is also mentioned to use others. He's able to conjure a multitude of razor sharp ice spikes which impale and freeze his opponents. He's also been shown using water magic and was able to easily neutralize Roswaal's most powerful Fire attack, without breaking a sweat. According to him, the more energy he gathers, the more likely he is to kill his opponent. Puck is stated to be the most powerful Fire Magic user, with the sheer power of his fire magic even surpassing even that of Roswaal.
- Shamak (シャマク): Puck's target becomes unable to sense where they are, however they can still feel the ground and sense what is happening to their body.
- Healing Magic: Puck summons water mana to heal the wounds of himself and others, however it only affects physical ones. Power varies by the skill and talent of the individual or partially that of the spirit if the caster is using Spirit Arts.
- Ice Flower (氷の花): Puck has demonstrated the ability to plant a seed within someone from which flowers of ice can later bloom. The flowers bloom by feeding off of negative emotions and sucking the host's blood and life force.
- Absolute Zero (絶対零度): Puck can freeze things to absolute zero temperatures causing the targets quickly crumble to pieces under their own weight. He was also able to release Emilia from being frozen at absolute zero by her own power for almost a hundred years, and only someone with equal power to Emilia could unfreeze her.
Mind Reading: Puck is capable of reading the surface thoughts or intentions of individuals he comes in contact to an extent. He can also communicate telepathically through this with anyone who has an affinity for Spirits even without Emilia being aware.
Unknown Ability: Puck is capable of freely and remotely communicating with Beatrice by using something similar to his telepathy, but only he is able to talk as it seems Beatrice cannot answer. The range of this ability is unknown, but it seems to even work across different dimensions as Puck was able to call Beatrice from inside the mansion while she was still in the Forbidden Library with Subaru.
Desertification: Puck can detect and remove curses according to Beatrice.
Mana Drain: Puck is capable of draining mana by touch. He is the only one besides Beatrice that knows this skill, though Reinhard has shown a similar ability at the end of Arc 1.
Star Beastification (星獣化 Seijuuka):
While normally staying in a small size, Puck's true form is a monstrous, 20 meter, glowing yellow eyed (in the anime it's been shown that Puck is able to keep his icy green eye colour in that form if he controls his temper) cat like beast which is dubbed "the Beast of the End". As he needs an incredible amount of mana to stay in this form, he forcibly drains it from his surroundings, causing them to freeze.
- Puck is capable of single-handedly defeating the Hakugei.
- According to the author, if he was a Re:Zero character then he'd want to be Puck.
- Puck was severely weakened during the time he was contracted to Emilia.
- Puck can't be more than 10 meters away from Emilia as part of their contract or the surroundings will start to freeze.
- Lesser spirits are scared of Puck so Emilia couldn't make a contract with them if Puck was present.
- Puck decided all of Emilia's hairstyles and clothes.
- Puck knows about Subaru's first love letter to his kindergarten teacher although it isn't explained how he came to know about this.
- In the author's character strength ranking in June 2014, the Beast of the End was ranked as the 5th strongest character in the series, though the list may have changed since then.
- At multiple times during the story, Puck can be observed using words from Japan or even English words. Roughly three years after his creation, during the era of the Witches four centuries ago, Puck was already observed using Japanese and English words–something no other character apart from Subaru and Al, ever did.
- Puck likes mayonnaise, noted by Rem after the condiment was introduced to the Mansion.
- If Puck died, everything other than Emilia would be frozen in a violent maelstrom. That is a part of his contract with Emilia.
- Puck, despite his knowledge of Japanese phrases and culture, was unsure if the mayonnaise that Rem and Subaru invented was safe.
- Puck is stated to be the first artificial spirit created by Echidna the witch, Echidna (artificial spirit) being the second and Beatrice being the last.
- "and am served by Puck, the Great Spirt that governs fire mana." Re:Zero Light Novel Volume 4: Chapter 4. Section 5.
- "In accordance with the pact, I'll be destroying the world now." Re:Zero Light Novel Volume 6: Chapter 4. Section 7.
- "Age: 420" Narou Blog
- "This is what I'm like now, but before my arms and legs were just a little longer, and if you can believe it, my face wouldda been handsome." Arc 4: Chapter 72. Section 3.
- "The reason I never spoke of forming a contract with you was because I made a vow." Re:Zero Prequel: Bond of Ice: Chapter 4. Section 8.
- "While Beatrice was harboring that impression, a voice unexpectedly reacher the back of her mind. It wasn't a voice that maintained a distinc form, but due to it being a voice with 'Power', it's intentions were conveyed clearly." Librarian Beatrice's Log - Restart: Chapter 1.
- "—Puckie is calling. It would seem this is an urgent matter." Re:Zero Light Novel Volume 2: Chapter 5. Section 7.
- "Magic healed them a fair bit, so Betty and I will lift those curses in no time at all." Re:Zero Light Novel Volume 3: Chapter 4. Section 2.
- "In this manor, only Puckie and I can perform such a feat. Even Roswaal cannot." Re:Zero Light Novel Volume 2: Chapter 4. Section 1.
- "Reinhard, Ram, Regulus, Sekhmet, Beast of the End (Puck)." askFM Q&A
- "Of the artificial spirits that were created by the "Witch" Echidna, in which Beatrice is included, only 3 exist in the world. The first of which is Puck, and the last is Beatrice." Beatrice's Everyone is Troublesome, I Suppose: Section 2.