Rex

Name: OSC#0001
Nickname: Rex
Gender: None (called by they/them or he/him)
Age: Unknown
Species: "Alien dog"

Abilities:
-Doesn't need to sleep
-Can control a kind of orange fluid. It's similar to blood in term of aspect, but that doesn't seem vital to them as they can get a lot of it out of their body without dying or even loosing strength
-seems extremely intelligent, but physically unable to orally communicate with Earth creatures due to their lack of vocal cords

Facts:
-They're the very first alien creature discovered by the Outer Space Life Research Program (OSLRP), this was officially called OSC#0001 (for Outer Space Creature number one). Their existence is kept secret to avoid mass population panic. They're studied by biologists, exobiologists and physicians in some protected place- some of them call them "Rex" affectionately
-Loose their right front paw before they were found by the OSLRP. The stump seems to have cicatrize in an incredibely clean way, but sometimes it bleed their orange "blood". This "bleeding" seem to be controlled by Rex, and is often used when they become aggressive (theorically, if they feel threatened)
-Is (literally) toxic: Prolongated physical contact to their skin, fur, or especially body fluids causes  mutations of the genome of Earth organism, thus causing death in the long term. Scientists use hermetical, anti-radioactivity like suits to approach them
-They surprisingly can eat Earth organisms, but only fishes. The scientific explanation is still unknown, and hard to study due to the invasive sampling method it'd need
-Strangely, they seem to accept their containment conditions. They're rather quiet, and seems pacific unless scientists try to take samples on them- except for an ingeneer, that they seem to tolerate (and even appreciate?) way more than the others for no apparent reason