Lord Mashima

is the name of a protecting deity in the form of at least two giant salamander-like creatures appearing in Jiraiya's novel, read by Tsunade in her Infinite Tsukuyomi dream.

Overview
The monsters called Lord Mashima were long, grey-skinned snakes with four short arms and round mounds, featuring a myriad of sharp teeth.

According to Kaya, "Lord Mashima" rests underground, protecting her village and its inhabitants, therefore, they praise it as a protecting deity. In its honour, a shrine at the outskirts of the village was built. This shrine features snake-like emblems akin to the monsters. Additionally, the shrine features a hidden underground entrance, leading to the cave where the deities dwelled.

The deity was apparently treated with much respect, since Kaya mentioned the villagers having lived peacefully to avoid enraging it. Also, Kaya prayed to it for her sons' safety and initially assumed their safe return was thanks to the deity's mercy.

In actuality however, the monsters attacked her sons multiple times and even swallowed Komichi alive. It was just thanks to the combined efforts of Team Asuma and Team Jiraiya that the children were saved and the monsters killed after a long, difficult fight.

Trivia

 * It's unknown if the term "Lord Mashima" refers to the monsters as an individual name or just to the monsters' race in general.
 * Ironically, mere hours after the deities were killed, the village was destroyed by a giant explosion, killing all inhabitants.