Tera Mutant (Upper Body) is a boss that appears in the Black Omen in Chrono Trigger. It periodically absorbs around 1,000 HP from the Tera Mutant (Lower Body), which takes next to no damage from all physical attacks, and absorbs all magical attacks. The Upper Body itself is not very threatening as long as the party is wearing protection against Confusion. The Upper Body takes next to nothing from basic attacks, and basic attack techs, but elemental attack techs, such as Crono and Frog's double tech Lightning Rod, will do effective damage to the Upper Body. Magical attacks are also effective. If the Lower Body dies, it will cast Halation which sets HP to 1 for all party members
In the SNES version, the name of the monster was "TerraMutant"; Terra being the Latin word for the planet Earth. However, the name translates from the original Japanese to "Tera Mutant", and is named as such in the more accurate DS script. Tera is a prefix used in the metric system which denotes 1012, or 1,000,000,000,000 (one trillion). Appropriately, this enemy is fought after the Giga Mutant is destroyed (giga, meaning 109, or one billion, comes before tera).