ENY is a varible that HTC has assigned to all planes, vehicles, and PT boats. The ENY values set in an arena are a key part of the perk points system. ENY is short for vs enemy. ENY values are also used in Side balancing the Main Arenas.
When in the hangar and viewing the list of aircraft and vehicles on the clipboard, you will see that each has an ENY value between 5 and 40. The ENY value represents the overall effectiveness in combat of the aircraft/vehicle. A low ENY value represents high combat effectiveness. Subsequently, the OBJ values are used for determining perk points earned vs objects.
So, for instance, aircraft with an ENY value of 5, like the La-7 or the N1K2-J, are regarded as having higher combat effectiveness than aircraft with an ENY value of 40, like the C.202 or the A6M2. These examples are in the Late War Main Arenas - aircraft and vehicles in the Early War Main Arena and Mid War Main Arena often have different ENY values.
ENY values are the basis for calculating the perk points you win. Essentially, the points you earn are based on the ENY value of the plane/vehicle you are using, divided by the ENY value of the plane/vehicle you killed. A high ENY value aircraft that kills a low ENY value aircraft scores high perk points; if the low ENY aircraft shoots down a high ENY aircraft, the perk score is low. See Perk points for details of the calculation system.