Heat oil in a large pot or Dutch oven over medium heat.
Add cubed bison in batches, browning well on all sides.
Remove browned pieces and place in a large bowl until all buffalo is browned well.
Return browned bison to pot with whatever juices collected in bowl.
Add onion and cook for about 2 minutes, stirring often.
Add tomato paste and continue stirring until paste no longer smells raw (Your nose will know, the paste will start to smell a bit sweet and the aroma will deepen.)
Add tomatoes, tomato sauce, Ancho chili, chili powder, cumin, paprika, garlic powder and beer.
simmer for 30 minutes and taste for seasoning. (it will still taste bland at this point, just make sure the amounts are close.)
Add butternut squash and simmer 45 minutes to 1 hour or until squash is just about fork tender, stirring occasionally to avoid sticking.
Add remaining ingredients and simmer uncovered for 1 hour, stirring often to prevent burning.
Add beef stock or water as needed to achieve desired consistency.
Season to taste.
Simmer uncovered for an additional hour, adding liquid if necessary.
Allow to rest 15 minutes before serving.