What Became of Ludo's Rat Army in Star vs. the Forces of Evil
The rat army—hundreds of small, identical brown rats with red eyes that Ludo enslaved using his corrupted wand fragment (influenced by Toffee)—was a major force in Season 2, helping him steal corn, rebuild ruins, and conquer Butterfly Castle in the Season 2 finale "Starcrushed."
Canon fate:
Their loyalty was tied to the wand's dark magic and Ludo's control (possibly amplified by a rat leader who delusionally believed he was Ludo after a head injury).
In "Starcrushed," the Magic High Commission (led by Rhombulus) storms Ludo's stronghold; Rhombulus crystallizes/freeszes many rats on-screen while searching for Glossaryck.
After Toffee possesses Ludo and is defeated in "The Battle for Mewni" (Season 3 premiere), Ludo loses the wand, his kingdom, and all control.
The rats are never seen again after Season 2. With the loss of magical influence, they likely abandoned Ludo, scattered, or reverted to ordinary wild rats (similar to how other minions deserted him previously).
No explicit on-screen resolution—it's an unresolved "What Happened to the Mouse?" element, like Ludo's original monster army after their castle's destruction. The show shifts focus to bigger threats (Meteora, Mina, magic's destruction), and Ludo's arc becomes more personal/isolationist.
By the finale "Cleaved," Ludo is shown rebuilding his family castle with his siblings (including Dennis), living a quieter life—no rats or army in sight.
In short, the rat army disbanded after Ludo's defeat and loss of the wand, with many possibly neutralized by the MHC. Their disappearance marks the end of Ludo's "king" phase.