1. Fritz the Cat (1972)
Fritz the Cat became the first animated film to receive an X-rating in the U.S. due to its explicit content, including sexual scenes, making it off-limits to viewers under 18. The film follows a college-age cat, Fritz, as he dives into a carefree and hedonistic lifestyle in 1960s America, exploring themes of hedonism and political awareness.
Despite the controversy surrounding its content and political backdrop, Fritz the Cat earned over $90 million worldwide on a modest $850,000 budget, becoming the highest-grossing independent animated film of its time.

2. Tarzoon: Shame of the Jungle (1975)
Released in 1970, Tarzoon: Shame of the Jungle is set in the African jungle known as Bush Country. The plot follows the protagonist as he embarks on a mission to rescue his girlfriend, who has been kidnapped by a gang with a peculiar obsession with giant genitalia, and taken to Queen Bazonga, a woman with 14 breasts.
The film features voices from comedy legends John Belushi and Bill Murray, but its adult themes and explicit content make it inappropriate for children. New Zealand banned the film in 1980 due to its unsuitable material.

3. Mary and Max (2009)
Mary and Max is an Australian stop-motion film that tells the story of an 8-year-old girl from Australia who has an alcoholic and obese mother. The film explores heavy themes such as abandonment, depression, loneliness, autism, obesity, sexual frustration, suicide, and anxiety. Mary and Max is definitely not suitable for children.
Nevertheless, the film is deeply moving and realistic, earning acclaim from critics and securing a nomination for Best Animated Feature at the Academy Awards.

4. Waking Life (2001)
Directed by Richard Linklater, Waking Life is a philosophical science fiction film about an unnamed man who wanders through a dream, encountering a variety of people. The film delves into the meaning and purpose of life and the universe, exploring a wide range of philosophical topics including the nature of reality, dreams, free will, and existentialism. Although animated, the film is best suited for adults due to its discussions of sensitive topics like politics, labor, and the concept of human rebirth after death.

5. Waltz with Bashir (2008)
The film took over four years to complete, blending classical music, realistic animation, and surreal scenes. It became the first animated film to be nominated for Best Foreign Language Film at both the Academy Awards and the Golden Globe Awards. The animated feature recounts the traumatic memories of a soldier who experienced the 1982 Lebanon War.
From the start, director Ari Folman decided to make this film in animation to depict the brutality of war and its consequences on humans through a completely new medium. With a dark, harsh tone, the work portrays the relentless torment of the veteran, haunted by his violent past and the deaths of innocent civilians he witnessed. The film is filled with scenes of bombings, gunfire, and bloody killings that are suffocating and terrifying.

6. Akira (1988)
Based on the eponymous manga, Akira is a science fiction epic set in a dystopian Tokyo in 2019, following World War III.
The story revolves around a secret military project that involves a member of a biker gang and a group of psychotic individuals. Widely regarded as a landmark in Japanese animation, Akira is considered one of the greatest animated films of all time. Since the early 2000s, Warner Bros. has attempted a live-action remake, though it has yet to be greenlit.

7. ParaNorman
ParaNorman is widely regarded as one of the best zombie-themed animated films, though it's definitely not suitable for children. The story follows a boy who can see the spirits of the dead, with a twist: the dead deliver messages about monster attacks, zombies, and witches, making for a chilling experience.
Moreover, the detailed stop-motion animation style of ParaNorman amplifies the horror elements, adding to the eerie atmosphere. It's clear why this film falls under the category of animated films not meant for younger audiences.

8. Watership Down (1978)
Based on the novel by Richard Adams, Watership Down follows a group of rabbits on their journey to find a new home as death and destruction loom nearby. The film is shocking not only for its violence and the bloody hunting scenes, but also for its dark themes, making it unsuitable for children.
However, this darkness helps the film perfectly capture the symbolic religious themes of the novel, securing its place as one of the finest adaptations of a book ever made.

9. Persepolis (2007)
Persepolis is an animated film based on the memoir of Marjane Satrapi. It follows the journey of a young woman in 1970s Iran as she witnesses her country fall under the harsh rule of an Islamic regime. The film was widely praised by critics and even earned an Academy Award nomination for Best Animated Feature.
Though there are no explicit scenes that would shock or disturb young viewers, Persepolis is undoubtedly a film aimed primarily at teenagers and adults who can understand the complex coming-of-age story of the protagonist, Satrapi, as she navigates the turmoil of growing up in a repressive society.

10. Paprika (2006)
Based on the novel of the same name, Paprika is an adult-oriented Japanese animated film filled with vibrant, dreamlike imagery. The plot revolves around a device that allows its user to record and watch their own dreams, or even those of others.
The device is stolen by a thief who uses it to invade people's minds, with the intent to plunge the entire world into a shared dream. Though there were plans for a live-action adaptation, those were indefinitely postponed after the release of 'Inception,' which explored similar themes.
