Chem is a koopa with Earth bending capabilities. His appearance looks like that of a Soopa Striker from Super Paper Mario, however the design is all he shares with them as Chem is a special case thanks to his ability to manipulate earth elements. In Super Mario Bros. Super, Chem makes an appearance as some sort of leader of a forest and protects his comrades from Mecha Sonic.

Voice: Have his voice exactly like how it's portrayed in the episode. I'll leave a link here for reference.

https://www.youtube.com/watch?v=TxFwhZYot9A&t=396s - Skip to 6:28 for Chem's voice.