Tinnos Mutants

Tinnos Monsters are among the hardest enemies to defeat in Tomb Raider III. They are found only in the Lost City of Tinnos level, and always attack in pairs or in threes. They launch harmful energy balls from their tails. It takes three Rockets (the weapon was designed with these enemies in mind) over around a dozen Desert Eagle shots for them to die. When using a non-explosive weapon to kill them, they will explode when they die.

These monsters slightly resemble the hideous and harmful big mutant scientists from the previous level, RX Tech Mines. Those mutants were halfway through their mutation and still wearing their RX Tech red uniform, so perhaps the Tinnos Monsters are fully mutated versions of these. Either this method, or they were creatures that made their way into the abandoned city and became mutated by the materials inside the meteorite crater.

Don't overlook the MP5 as a good weapon to use at a distance, and note that they use their claws on close rang, and the energy balls at long range or when Lara is hard to get to (such as standing on a block).