Extinction core brings Reapers to the game without having to play the Abberation map.
Alpha Reaper King
Supreme Reaper King
The 'Volcanic' region of the map will spawn all Varities of Reaper.
On the Center map, they can be found patrolling the black sand shores of both the large and the small volcanic islands.
Killing Alpha and regular Reaper Kings will reward you with a few Reaper Androstenone Glands (red icon)
Killing Reaper Queens will reward you with a few Reaper Pheromone Glands (green icon)
In order to tame a Reaper King for yourself, you must lower a Reaper Queen to under 10% health, at that point you need to turn off your light source and the Reaper Queen should glow with a red color. Once that happens you need to dismount, approach the Queen, possibly withstand a tailswipe, and then she will grab you and begin a sequence. You will be injected with a reaper king baby and within a few hours, it will be born, you have a set time to gain experience for your character that will pass along to the baby. Before it is born you must consume a female reaper gland so that the baby does not attack you.
Once you have a fully levelled Reaper King you must defeat an Alpha Reaper King. This will give you the recipe for an Alpha Reaper King, you have to collect many reaper glands as well as black pearls and put them in the inventory of your fully levelled Reaper King and craft the recipe in order to upgrade it.
The same formula applies when you want to upgrade your Alpha Reaper King into a Supreme Reaper King, however this is one of the last things you do in Extinction core