H.W.
I'm more of a 'teach instead of punish' type parent, so here goes:
No more threats, mama. Every time he gets out of bed, take him back to bed. No talking, no attention, no anger. Your face stays emotionally-neutral. Your body is relaxed. You do not talk to him. You do not make eye contact with him. He gets *zero* reaction from you, just a trip back to bed.
Be prepared that teaching requires patience. When I did this with my son, I planned my evening around it and walked him calmly and silently back to bed about four times. I actually took a book into the hallway with me and camped out outside his door, so the minute he popped out, I was putting him back to bed. (This way, I didn't feel like my evening was interrupted. It was simply a 'teaching' time.)
The second night, he tried it a couple times.
By night three, he tried it once.
No real problems after that.
Your son is younger, and you may have a few 'teaching nights' in store for you. Just remember, if you lay this groundwork now and stay calm, it will stop being a game for him. There's no payoff because there's no attention or emotional response from you. It gets boring for them after a while. They learn- "I get up, I get put back in bed".
Good luck-- and wishing you plenty of patience!