How do I get Ride Together Die Together?
I fought Pimon & Tumba both while on True Vault hunter mode. If I remember correctly Pimon is a stalker & Tumbba is a skag. They can also spawn in Normal Mode (Thanks, @SheDevil).
They appear on the field outside of preserve cells (where bloodwing was kept).
I will suggest weaken them both and take them down with a grenade or something.