I have found a way to “make” rivals

I have found that if you let say, a tank or harvester kill you, there is about a 90% chance it will turn into a rival.

It is common knowledge that Rivals can spawn out of those enemies that kill you.

Also, there is 2h in-game cooldown period before a new rival can spawn in the same area again.

Further reading: How to get a rival to spawn (guide)

Have you no pride, young man? Tanks and Rivals should be swiftly assassinated, not indulged…