Yo-kai Arks

A is a small, key-shaped item used to summon Yo-kai from the Yo-kai Watch Elder. These Yo-kai Arks first debuted in M04 and the Shadowside anime. They are said to be the successor of Yo-kai Medals, featuring Lightside and Shadowside Yo-kai on both sides.

Rare versions with different colors also exist. The levels of rarity that range from common, to extremely rare, are Normal, Rare, Extreme Rare, Super Extreme Rare, and Ultimate Rare.

Most of the Normal Arks have a clear color and a regular holo foil, while Rare Arks have a clear color and a glittering holo foil, and Extreme Rare Arks have the colors of their tribes, as well as glittering holo foil.

There are also Shining Arks that are equal to Super Extreme Rare ones, and Gold Arks that are equal to Extreme Rare ones.

In the Yo-kai Ark 0 pack, there also are Yo-kai Arks that have a Lightside form, but also a Godside form, for use with the Yo-kai Watch Elder Jin parts, that can be found in the DX Yo-kai Watch Elder Zero & Jin Power-up Kit. These are of a white base colour, with a rainbow holo for the Godside forms.

As of Yo-kai Watch!, there are Yo-kai Arks that retain the Lightside, but the Shadowside is instead known as a "Onechanside".

Information
Yo-kai Arks represent the feelings that connect Yo-kai and humans. Just like Yo-kai Medals, they are given to select people once they fulfill a specific Yo-kai's needs.

Yo-kai can be summoned via the Yo-kai Watch Elder by putting the Ark into the keyhole, and saying the summoning chant while the Yo-kai appears in sight.

It was originally thought that the Arks were successors to the medals, however, due to their inclusion in Forever Friends and Yo-kai Watch!, they existed in the past as well.

Shadowside Arks
Arks that debuted as of the Yo-kai Ark Zero pack require the DX Yo-kai Watch Elder to be updated to Version 2 or above.

As of Version 2, some of the Arks (like the Gold Yo-kai Arks) are updated with new voices added. When using the Jin parts from the DX Yo-kai Watch Elder Zero and Jin Powerup Kit, the Gold Yo-kai Arks have different voice lines, used when in Godside. (This only pertains to the Gold Yo-kai Arks from the World Hobby Fair exclusive Yo-kai Ark pack.)

Godside Arks
In order for the Godside Arks to be read, the DX Yo-kai Watch Elder needs to be updated to Version 2 or above. As well, to read the Godside part of the Arks, the DX Yo-kai Watch Elder Zero and Jin Powerup Kit is required, using the Jin watch parts.

Onechanside Arks
As of the Yo-kai Ark K1 pack, in order for these Yo-kai Arks to be read, the DX Yo-kai Watch Elder needs to be updated to Version 3 or above. The DX Yo-kai Watch Elder Ver. K is already preloaded with Version 3.

Trivia

 * In early portrayals of the Arks, including their debut in the 4th movie, they had the insignias of the old Yo-kai tribes. These were later replaced by the symbols of the Shadowside tribes.
 * For Yo-kai Watch!, most of the original Yo-kai that also appeared in Shadowside still retain their Shadowside Tribes in the new series.
 * The only Shadowside Yo-Kai that don't have real life arks so far are Mitsumata Mizuchi, Hamham, Kiborikkuma, Choky and Kawauso.
 * Several Onechanside Yo-kai don't have arks so far, they are Insomni, Little Charrmer, Mochismo, Shadow Venoct, Snartle, Shogunyan, Komashura, Jabow, Reuknight, Corptain, Silver Lining, Krystal Fox, Master Nyada, Noway, Mimikin, Mirapo, Robonyan F (Who only has a Miracle Ark), Wiglin, Steppa, Rhyth, Melonyan (Who also only has a Miracle Ark), Walkappa, Cornfused, Sighborg Y, Wobblewok, Deadcool, Ogralus, Orcanos, Gilgaros, Dazzabel, Petty-Cake, Koma Kaachan (She only appears as Komasan's Onechanside), Goofball, Wotchagot, Pride Shrimp, Grubsnitch, Poofessor, Thornyan, Faysoff, Demandi, Toiletta, Ballin, Snailspace, Chippa, Rhinormous and Hornaplenty.
 * Uula, Gashadokuro (Shadowside), and Onimaro Leader don't have any either though they may be anime exclusive, altough, unconfirmed
 * Oniou Rasen and Kaodeka Oni don't either but Oniou Rasen may be because he's a Boss Yo-kai and Kaodeka Oni are simply just humans inspirited by Onimaro who also don't have Arks (Not counting Ogu, Togu & Mogu) possibly due to them being minions.