Man, I've wasted way too much time brainstorming prehistoric murder-bird OCs. For me, the key is subverting the 'lab monster' trope everyone goes for. Instead of an escape, what if the indoraptor wasn't an experiment gone rogue, but a deliberate, late-stage prototype that got loose before they could fully program its obedience? Its backstory isn't about being a failed weapon, but an unfinished one. That creates this terrifying potential—maybe it retains some fragmented, glitchy command codes that can be triggered, making it unpredictable in a different way. You get a creature that's both hyper-lethal and occasionally, bizarrely compliant, which is way scarier than pure chaos.
Another angle I love is the 'living paradox' idea. The indoraptor is a genetic mosaic, right? So lean into that. Maybe it has conflicting instincts spliced in—velociraptor pack-bonding urges clashing violently with the solitary, territorial nature of the T-rex lineage. Instead of a clean killer, you have an animal that's profoundly mentally unstable, driven by impulses it can't reconcile. Its backstory could involve it attacking its handlers not out of malice, but because a misplaced maternal instinct towards a human scientist triggered a catastrophic predatory sequence. The tragedy is baked in from the start.