Doki! Doki! Yuuenchi: Crazy Land Daisakusen is a Nintendo Family Computer video game where players control a boy with a helmet who kicks balls at enemies. The more damage he takes the more damage he does to enemies.
The game was originally called Doki! Doki! Yuuenchi (ドキ!ドキ!遊園地?) in Japanese, meaning "Thump! Thump! Amusement Park". Doki (ドキ?) is a Japanese onomatopoeia. The game was remade into The Trolls in Crazyland. Although it was previously to be released as Crazyland, it was then changed to feature the popular Troll dolls; this version was released only in Europe.
Source: Wikipedia, "Trolls in Crazyland", available under the CC-BY-SA License.