It uses Earthquake, so Porom should cast Float to avoid it. Its only other main attacks are strong physicals, which can easily be healed. However, if one casts magic on the Tyrannosaurus, it will counter with a high-powered magical attack of its own - it will counter Fire magic with Flame, Ice magic with Ice Storm, and Lightning magic with Lightning. Thus, physical attacks are advised to defeat it, although even its counterattacks are not that strong, and only Ice Storm does notable damage. Flare and Holy, however, are not countered, and given your magic using party members (Palom, Porom, Rosa, and/or Rydia) are high enough level, you should cast these. When vanquished, the Seraphim's Mace, Porom's ultimate weapon, may be be collected from the treasure chest the Tyrannosaurus was guarding.
[view·edit·purge]The Tyrannosaurus is a genus of dinosaur that lived during the late Cretaceous period. Its scientific name means "tyrant lizard". The species Tyrannosaurus Rex is one of the largest land predators ever known and means "king of the tyrant lizards".