GuldThunder

GuldThunder (ガルドサンダー): A red Fenghuang monster in a Phoenix-shaped helmet. It can attack with its retractable tail and use fire attacks. It devoured Yuichi under Kanzaki's orders when Yuichi turned down Kanzaki's offer. It was later used by Kanzaki to attack Kamen Rider Raia. Destroyed by Raia's Hide Venom. Originally designated to be the Contract Monster of Yuichi in concept arts in the event that Yuichi accepted Kanzaki's offer.

Kamen Rider Decade
It is shown briefly fighting Kamen Rider Ryuki alongside Omegazelle and Zebraskull Bronze.