As with the other Sengoku and Genesis Riders, Kamen Rider Knuckle's forms are called Arms (アームズ Āmuzu). His Sengoku Driver plays American rock & roll music and emits a guitar riff sound before every transformation, while her personal Lockseeds are styled in pure English with a "Mr. [Adjective/Noun]" theme.

By pressing the Sengoku Driver's Cutting Blade down on the Lockseed after transforming from one to three times, Gaim can activate one of three finishing moves based on his current Arms form:

　・Squash (スカッシュ Sukasshu)
　・Au Lait (オーレ Ōre)
　・Sparking (スパーキング Supākingu)

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Ride Wear
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The Ride Wear (ライドウェア Raido Uea) is Knuckle's default form undersuit which is briefly seen during Knuckle's transformation sequence, before the Armor Part attaches or when she changes Arms. However, this form is completely vulnerable to any incoming attacks when shot at directly in the suit, rather than at the Arms that is descending down on the Rider.

Unlike the original Kamen Rider Knuckle, his Sengoku Driver is also featuring its own Rider Indicator (ライダーインジケーター Raidā Injikētā) faceplate, despite being a mass-produced version. However, it can be replaced with extensions such as the Genesis Core Unit or Senyo Joint.

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Kurumi Arms
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"(Guitar riff) Kurumi Arms! Mr. Knuckle Man! (Three count bell ring with a cheering crowd)!"
－Transformation announcement－

Rider Statistics

・Height: 204 cm.
・Weight: 107 kg.

Ability Perimeters

・Punching Power: 8.1 t.
・Kicking Power: 9.0 t.
・Maximum Jump Height: 26 m.
・Maximum Running Speed: 100 m. per 5.9 sec.

The Kurumi Arms (クルミアームズ Kurumi Āmuzu, lit. "Walnut Arms") is Knuckle's  walnut-based default form. Accessed through the Kurumi Lockseed, this form bears the Knuck Met (ナックメット Nakku Metto) helmet with the Knuck Eye (ナックアイ Nakku Ai) visor.

While assuming Kurumi Arms, Knuckle dons the Kurumi Armor Part (クルミアーマーパート Kurumi Āmā Pāto, lit. "Walnut Armor Part") and her Arms Weapon is the Kurumi Bombers.

In this form, Knuckle's offensive stats are lower than Gridon's. He has better agility stats, jumping higher and running faster than the aforementioned Rider.

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Jimber Marron Arms
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"(Guitar riff) Mix: Kurumi Arms! Mr. Knuckle Man! (Three count bell ring with a cheering crowd) Jimber Marron! Ha-Ha!"
－Initial transformation announcement－

"(Guitar riff) Mix: Jimber Marron! Ha-Ha!"
－Standard transformation announcement－

Jimber Marron Arms

Jimber Marron Arms (Shells-off)

Rider Statistics

・Height:
・Weight:

Ability Perimeters

・Punching Power:
・Kicking Power:
・Maximum Jump Height:
・Maximum Running Speed:

Jimber Marron Arms (ジンバーマロンアームズ Jinbā Maron Āmuzu) is Knuckle's walnut/chestnut-based fusion form, which accessed through the simultaneous use of the Kurumi Lockseed and Marron Energy Lockseed.

While assuming Jimber Marron Arms, Knuckle dons the Jimber Marron Armor Part (ジンバーマロンアーマーパート Jinbā Maron Āmā Pāto) and his Arms Weapon is the Marron Bombers.