The 4th gen mascots use the same slot as normal pokes, but their PID is generated as if they have a forced male gender. It consumes the same number of PID frames as a gendered Pokemon even though they actually don't have a gender.
Best to experiment first with one that you don't care so much about, I'd say.
Yeah, my PoS laptop runs windows so I use RNGR. The process was actually really easy thanks to a guide another Smogon user drafted. It took me a failed legend RNG to figure out the stating frame was different for them, but I managed to get a 31/31/31/xx/31/31 Jolly Thundurus today. DR abuse is surprisingly easy. Thanks for the help Chiizu :3
Oh yeah, I also wanted to ask, do the other legends from the DR follow the same process? IVRNG starts at frame 21, PIDRNG has an off set of 5, etc? The only difference would be to add 1 to the starting PIDRNG and not 2 since the other legends are genderless right?
Yes, the genies basically throw out the first frame. That's why there is a separate encounter type for them in PPRNG. There are other differences as well, so you should always run a search with exactly the parameters you will be RNGing to ensure you don't have these kinds of problems.
Although I guess the fact that you are talking about frame 21 and slot 2 for legendaries means that you can't use PPRNG and are doing it by hand... I know people have been successful at it, but it's not for the faint of heart.
Quick question, Dream Radar legends are slot two right, with a stating frame of 21? I tried to RNG my Tornadus after doing a test run with the seed and it failed. By pure coincidence, the test run I did happened to transfer 2 pokemon over, the first one had the IVs and nature I wanted and the second one I ignored. I then used the same process for Tornadus and it came out lax and with horrible IVs. I then noticed that this matched the slot 2 pokemon that was transferred over during my test run. When I did Tornadus I had no other pokemon to transfer and no items. I transferred first than went strait to Tornadus and tried to RNG him. I just want to make sure I have this down right so I don't wast Thundurus too.