MechaRaptors

Requires heavy
an animal associated with, or symbolizing, power:

Dinosaurs. Some bright spark always brings them back. Some other moron wants to "improve" on them. And it always goes exactly as you'd expect.

Mecharaptors are biologically enhanced dinosaurs - encapsulating a variety of species. They were bioengineered in the mid-21st century from fossil remains, spliced with ostrich, crocodile and even honey badger DNA.
Quickly outlawed after the Din-escapades of the following century (you thought crocodiles in the sewers were bad) the only Mecharaptors that remain today are illegal animals that were taken from labs or captured from wild, escaped breeding pools. They are typically enhanced with biotechnology including hydraulic limbs, steel tipped teeth and claws, and even laser eyes and fire jets. In some species, tail whips re common, although these are known to do as much damage to the animal itself as to their prey.

Mecharaptor fights take place in underground locations - sometimes literally, alike in the sewers, an sometimes in abandoned warehouses. They are often sources of gambling and income for gangs. There are different weight classes for Mecharaptors, measured in real-world animal sizes. From the chicken-weight, to dog weight, through horse- elephant - weight, and, most terrifyingly, mammoth weight classes (only a few stories of those fights remain as they tended to topple buildings and blow the cover to the cops).

Unsuccessful Mecharaptors often become prey for their more successful sparring partners, but Mecharaptors breeding - even of unsuccessful Mecharaptors  is also huge business. Police raids often turn up bath tubs full of tiny dinosaurs or unhatched eggs (which are worth a whole buttload of credits on the black market). Biotech labs in backstreets sometimes have suspiciously large or aggressively looking inserts, and it's best not to ask about that kind of tech, if you wat to wake up from the anaesthesia.
Different MechaRaptors - including the Steg-techsaurus, the velociRAMster and the Tyrannosaurus GigaRex are a common sigil for street gangs, drug runners and organized crime syndicates.