In Mexico, a Sauroposeidon activates when the Card Capsule falls in a river and hits a rock. It roars. Meanwhile, at Area Fifty-Something, Dr. Cockroach is reading Fire and Water when the Dino Holders go off. He slides down the chute to his lab. When the others get there, Link asks his traditional "Where is it?" "Mexico again. Seriously, how many cards can fit in there?" They then transport. When they get there, they see some trampled trees by a river. "So what did that?" "Doc?" Dr. Cockroach growls before turning around. "It's a Sauroposeidon. BOB!" "Monster Slash! Bring in the thunder, Columbian Mammoth!" Marven's summoning sequence plays. The Sauroposeidon hits with Shockwave. It hits with Aqua Javelin. it uses Ocean Panic, summoning the Ophthalmosaurus, who attack Marven from the river. The Sauroposeidon hits with Neptune Stream. "Blitz Counter!" it's a hit, defeating the Sauroposeidon. Because their user was defeated, the Ophthalmosaurus turn back into a card and blow away. BOB picks up the remaining cards and gives them to Link, who names it Stomper. When he puts Stomper's card into the Dino Holder, Merman is sent into storage. They then go home, where Dr. Cockroach determines Stomper to be a 17 on the Power Scale. Tally sequence. "Now that we've got a Sauroposeidon, we've got a total of 49 creatures."
This is the fifth time a card was found in Mexico, counting the Anuro Tornado card. This is referenced in the beginning by Dr. Cockroach