I will repeat here my reply from Discord just in case anyone else is wondering the same thing.
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The D-Gater Backer pack is a Backer pack from the Newcomer campaign:https://my.em8er.com/perks/campaign/5
M3 is a previous campaign that has been closed since it ended on IndieGoGo in July 2017.
The only way to get your hands on an M3 pack now is to find a fellow Reaper who has an M3 One Dollar Club pack to gift.
OR, if Grummz and Ronyn have any left, they may raffle some off during Chief Chats.
Once you have your hands on an M3 One Dollar Pack, you'll need to upgrade to a minimum of the Scout Backer Pack ($15 USD) to receive the single-seater Python Bike skin as a thank you for upgrading.
If you want a copy of the game when released, that would be an upgrade to the Deepscanner Backer pack ($35 USD).
To get the pet from M3, you'll want to upgrade to the Omni Ace Backer pack ($500 USD). For reference, the pet is described as follows:
"Turret #2 Pet! (This is a 4 legged, walking turret that fires cosmetically, it is an homage to a certain game cinematic - Final Game)."