Badaxtra

Badaxtra was a powerful, mutated, axe-bladed kaiju from Japan, accidentally created during the 1960s by atomic science gone wrong. Armed with axe-bladed feet, tail and head, it can simply trample and/or slice any opposition. It was later captured and sealed in Mt. Fujiyashiyame by brilliant scientists. In the episode Last But Not Beast, after decades of being imprisoned in Fujiyashyame, it was accidentally released by Dexter when he lost control of his special PEZ Missiles, launched by his Robo-Dexo 2000. Badaxtra then wreaked havoc on the capital of the Land of the Rising Sun, eliminated the Robo-Dexo, the EDF, and the Justice Friends. Later, with the help of Toshi's advice about united hearts, his family, and Monkey, Dexter promptly rendered Badaxtra extinct with his Multi-forming Megabot, but not without suffering initial technical difficulties. Badaxtra's vocal effects were provided by Frank Welker.

Trivia

 * Badaxtra's origin is very similar to Toho's legendary Godzilla. Both are birthed from the nuclear fires of the atomic age - but while Badaxtra is permanently killed, even death cannot stop Godzilla, as evidenced by the movies wherein he has regenerated himself on numerous occasions.
 * Badaxtra is likely a nod of Godzilla.
 * He bares a slight resemblance to the Gamera villain Guiron, which had a knife for its head.