The Castro Monstruo is a pickup Monster Truck consisting of a Castro Robusto body on a Monster Truck chassis. It is available in the Speed Expansion Pack, where you must complete the Speed Weekend successfully in order to unlock it.
- The slats in the grill of the Monstruo are vertical, as opposed to the Robusto's horizontal grill.
- "Monstruo" is the Spanish word for "monster".
- Instead of a mid-mounted engine underneath the body (like other monster trucks), the Monstruo has one positioned in the truck body's loadbed.
- It also appears in MotorStorm RC as a remote control monster truck.
- Also in Motorstorm RC, the Monstruo's lightning bolt livery is based off of an AI-exclusive livery for the Robusto in the first Motorstorm; it is used by the AI driver Ivan McCloskey.
- Again in Motorstorm RC, the flame livery for the Monstruo is based off of the flame livery for the Robusto in the first Motorstorm, minus the sponsor stickers.
- It bears a resemblance to the Castro Robusto and the Castro F80.
- One of the liveries (the blue and yellow one) clearly states "Turbo Diesel", indicating that this may well be a diesel powered monster truck however, just like the Atlas Earthquake, it sounds identical to others in its class.