In his last killing, God forced the Israelites to kill each other. (The Levites volunteered for the job of "being on the Lord's side" by killing their family, friends, and neighbors for God.) The resulting death toll was 3000.
But this didn't quite satisfy God. He needed to kill some more. So he sent a plague.
The LORD plagued the people, because they made the calf, which Aaron made. Exodus 32:35
The Bible doesn't say how many people God killed in this plague. I'll guess 1000.