Animal Crossing-e Series 2
One of the cards in the second series of Animal Crossing e-Reader cards, specifically card D04, is a Pikmin Pattern card. Scanning the card into the game will unlock the pattern for the player's house.
April 29, 2004
One of the obtainable treasures in the game is the "Gyroid bust", which is similar to the Gyroid from Animal Crossing.
Both items are actually based on the haniwa, ancient Japanese statues, so the reference is arguable for the Japanese version of the game, but the "Gyroid" name used in international versions of both games is original to Animal Crossing, making the reference intentional at least in those versions.
Animal Crossing: Wild World
November 23, 2005 (game release); July 2006 (item release)
The game features a Pikmin item, which consists in a small box with three Pikmin planted in soil: a blue Pikmin with a leaf on it, a red Pikmin with a flower on it, and a yellow Pikmin with a bud on it. When touched, it says the word "Pikmin", sounding similar to the sound that plays at the start of Pikmin or Pikmin 2.
This item is normally unaccessable in the game and was only given at special events in Europe in July 2006, and in Japan in July 2007.
Animal Crossing: City Folk
November 16, 2008 (game release); February 6, 2009 (PAL item release)
To celebrate the release of New Play Control! Pikmin 2 for Wii, the Red Pikmin Hat item was added to the game. Players who received it can buy it from Tom Nook's Store for 400 Bells.
In Japanese and American versions of the game the item is accopanied by a letter from Nintendo, however this was changed in the European and Australian version to a letter from Olimar himself, creating an in-universe link between the two series.
On July 20, 2009 a spaceship item called Dolphin Model was released only in North America to celebrate the 40th anniversary of the Moon landing. The item is based on the SS Dolphin from Pikmin, only colored blue instead of red.
The game also features two additional Pikmin themed items in its code, though they're unaccessable without hacking: the Pikmin item from Wild World, and the Shiny Blue Pikmin Hat, a differently colored version of the Pikmin Hat.
Animal Crossing: New Leaf
November 8, 2012
The game features five items based on the Pikmin series, all available as Fortune Cookie prizes. These include the Red Pikmin Hat (simply called Red Pikmin) and the Pikmin item from the previous game, as well as new hat variations based on the Blue Pikmin and the Yellow Pikmin, and a recolored S.S. Dolphin model. Each item has a fortune related to it, with the hat ones referencing the respective Pikmin's powers.
Additionally, one of the special tree stump designs is based on the flower logo for the Pikmin series.
July 13, 2017
This game features compatibility with all amiibo released at the time in the Animal Crossing series, and scanning one will make the respective figure appear within the game as a collectable treasure. Since the figure needs to match the amiibo, the game is only compatible with specific amiibo, amiibo cards based on the same character won't be recognized and will only be considered a generic amiibo.
Compatible Animal Crossing amiibo, as they appear in the game, are:
Copyrights for both series are held by Nintendo.