TL//DR: Double box only, Main account hosts, Use map Crystal Lake Small, during loading cutscene use dummy account to scroll your friends list for your main account and press join game to quickly leave and join back to the main accounts game. Total time per match: roughly 2 mins 15 seconds, Aim to finish counselors first by not assigning the role of Jason to anyone
This method is based off of a comment and another solution i read (Credits and Thanks @Bobby Trippe) which helped me formulate an 'endgame' grinding plot. This is for those who just have to do the 1k counselor, 1k jason, and 1.3k kills/matches played. This is also for those who can double box the game on their own ONLY-you can do this with 2 people but 1 person won't get any progress, therefore making the other solutions your best bet.
The 'plan' itself: First, use Bobby's solution (read->glitch) to get the kills out of the way apparently this glitch is patched, but i still recommend going for bot kills (which takes a bit longer mind you) on the easiest settings, and then going for matches played. it goes faster that way imo
Solution for Gotta Kill Em All in Friday the 13th: The Game
Using his solution got me ~750 kills in maybe 4 hours, which is superb. I also capped off at 50 per match roughly, as afterwards Jason gets enraged which makes escaping somewhat longer, which is a slight waste of time that'll add up.
With that taken care of, all that is left are the 2000 total matches. First, go on the map Crystal Lake Small for the fastest loading time. From the game menu, hit start with both remotes (both xboxs) and then with the host, press cn_RB 4 times to go to the desired map. It is also worth noting that the account you want progress on NEEDS to be host, otherwise you won't get progress at all.
Once the match starts loading, pick up the dummy account's remote and wait for the ingame cutscene to start playing. Wait for it to play a bit (until the guy gets pulled off the deck into the water) and then go to your friends list, find your main account, and Press Join Game. This will automatically make you leave your current game with the dummy, go to the main menu, then go back to the hosts game. Then it will flash on screen 'you were kicked, Press cn_A " so simply press cn_A and boom, right back where you started. i would recommend Favouriting your main account so that it is right at the top of your friends list, making it take a little less time to scroll down the list.
The reason why i suggest letting the cutscene play in a bit is because from the main accounts POV, it still needs to load the rest of the cutscene, then finish the match and back out to the main menu. Backing out earlier in the cutscene doesn't actually save any time, and from personal experience it just made my game crash relatively often.
**Also worth noting here, that if, as the host, you assign the dummy account the role as Jason, when the account leaves and joins back they will no longer be assigned that role. Which is why i strongly suggest not assigning the role to anyone initially when grinding this: you will get progress on both the counselors and the Jason matches as the roles are assigned randomly. however once the jason matches are done the best strategy would ultimately be to use the dummy as jason and kill your main account.
Edit: after pressing start on both remotes, you can move the left stick to the left and it will highlight the assign Jason icon on the dummy account, so press A and voila you can get counselor progress. However, after a while it will, from the hosts eyes, say the 2nd account is still loading in, when in reality they are already in the lobby. Therefore, i still recommend going for the counselor matches first as the only way to fix it is to reset the game, which needlessly wastes time. Or, you could go to the main menu, Customize, Spawn Preferences, and then pick what you need to grind out (Pick Jason with the dummy to get counselor matches for the Main).
This is ideal for grinding out the achievement because the total time it took me to get 1 match done was 2 mins 14 sec roughly every time, which was a whole 20 seconds faster than the other method i was using (the other solutions) of getting the perk that gives the player a map upon starting the game up, teleporting there with Jason, and killing them. Doing this literally cuts out loading into the match at all, and it still gives progress for the main account.
By a quick numbers crunch, 2-3 entire extra matches can be played per hour at 26-27 per hour. This isn't exactly a massive timesaver, but in grand total it will shave off roughly 2-3 hours from boosting the achievement in comparison to going for the kills. Now, in terms of Jason, it might not be truly great as you still need to take the time to get all the kills, which ends up balancing out the matches more or less, but for counselors it is really worth while as all you need to do as a counselor is play the match through.
If anyone finds any optimizations for this, or has issues, please comment. Happy grinding ( :