Pipo Saru 2001 has only been released in Japan. A demo was released through McDonald's named the "Happy Disc". The levels were slightly altered to contain Fries and Burgers as life's and the levels re-designed to contain McDonald's balloons and Signs. A North American version was planned with the working title Ape Escape 2001, but it was canceled.
Piposaru 2001's Gameplay differs from the original Ape Escape gameplay outline. The left analog stick on the DualShock controller is used to control Spike's movement, but unlike the original game, the right analog stick was unused and the Face buttons were used to attack. The goal of each level is to use a vacuum cleaner to remove a required amount of pants off of the apes and put them into an oversized washing machine, while preventing the monkeys from re-obtaining their shorts or attacking the player. While sucking the pant off a monkey, the monkey can be fired into other monkeys to knock them out. Bomb tokens can also be collected to attack monkeys and bosses. The graphics were slightly improved yet very similar to the original game, with the same symbols throughout the game (such as the stage cleared symbol). Also (like the first), it was made for a broader audience from ages 5 onwards, unlike Ape Escape 2 & Ape Escape 3 which was intended for younger audiences. Also, Piposaru 2001 was the first game in the series to feature no other enemies excluding the apes.
The storyline is a simpler compared to the original game. Specter has made all the monkeys' pants dirty and Spike/ Kakeru has to wash them. Although the storyline & controls were simple, the levels of the game were designed rather well. It also featured many more levels than the original game. It has 36 stages while the original had only 19. Each level is timed. The storyline changed and is a similar game style to Ape Escape Pumped & Primed. There are five stages to complete, and then a boss battle in each level. Much like Pumped and Primed's layout.
The game features fewer characters than the previous games.
Spike/Kakeru - The red haired protagonist of the first game who defeated Specter.
Natalie/Natsumi - The Professor's granddaughter that assists Spike on his journey.
Professor/Hakase- The Professor who invented the pipo helmet, warp/time machine, and other gadgets.
Specter - The evil monkey who has attempted world domination. His intelligence is increased by the pipo helmet.
Pipo Monkeys- The common monkeys of the game series.
Source: Wikipedia, "Pipo Saru 2001", available under the CC-BY-SA License.