Thardus is a gigantic creature composed of rocks in the Metroid series, first appearing in Metroid Prime as a boss. It's a large, hulking rock and ice monster that was formed as a result of one of the Space Pirates' scientific experiments. The experiment, code named "Project Titan", was a test to see how the highly mutagenous Phazon would react in the presence of non organic materials. Thardus rapidly became too powerful to control and was sealed away in the Quarantine Cave of the Phendrana Drifts on Tallon IV.
Thardus is first encountered when Samus Aran enters the Quarantine Cave during her exploration of Tallon IV. Thardus forms its gigantic body composed of multiple rocks and block of ice held together by Phazon radiation before Samus' eyes and almost imediatly begins to attack her as it is extremely agressive. Thardus has three types of regular attacks, it can throw three destroyable rocks at Samus, generate a beam of freezing energy that can trap Samus or simply curl up into a ball and attempt to crush her.
During the fight, Samus is unable to use conventional targeting systems as they are disrupted by Thardus' enormous amount of natural radiations. Samus must use the Thermal Visor to detect his weak spot and shoot at them. Shooting them enough will expose Thardus' Phazon core, which in turn releases a wave of energy that will overload the Thermal Visor and forces Samus to switchh back to the Combat Visor if she wants to see anything. After repeating the operation three time to destroy three of its weak spots, Thardus will unleash an ice storm, making it hard to see in the Combat Visor. After the sixth weak spot is destroyed, Thardus will dispel the ice storm, so visibility returns to normal but in turn, Thardus will noticeably speeds up, as it only has one more weak point that must be attacked. Once defeated, the behemoth leaves the Spider Ball behind, which allows Samus to progress further.
Metroid Prime Pinball
"The Phazon radiation given off by Thardus negates auto-targeting systems, preventing lock-on. It may be possible to acquire alternate targets with a different Visor. The chaotic nature of Phazon irradiation leads to instability in its structural integrity. Thardus can encase targets in ice, and its colossal size and strength make it a formidable opponent."
Map Station (Phendrana Drifts)
"Project Titan specimen is immobilized in Quarantine Cave. Relocation is recommended due to increased violent activity."
Research Lab Aether
"East Quarantine Cave has been secured. Specimen remains in the Quarantine area. All experiments have been suspended pending pacification of area."
"Quarantine specimen exhibits highly aggressive behavior. Its body structure, composed of Phazon ore, appears nearly invulnerable. This has rendered our efforts to train and discipline subject useless."
"Project Titan is suspended indefinitely. Security breaches resulting in massive casualties have occurred. Access is strictly prohibited until further notice."
"Research on Tallon IV is expanding into new areas. Pending stabilization of the Thardus venture, we will expand Inanimation research to include other native Tallon IV materials."
"The taming of Thardus continues. Barring unforeseen attacks, it can be installed on Phazon mine patrol by Lotus Milestone."