I suppose I could call this God's 30th to 89th killings, since there must have been 60 separate killing events. If God did the killing himself, he could have done it all at once. But he was relying on people to do his killing for him, so it must have taken some time. First the Israelites had to go to city 1 and kill all the men, women, and children that lived there, then on to city 2, and so on up to the 60th city. But since the Bible lumps all 60 killings together, I will too.
The Bible doesn't spend a lot of time on these killings. Only 4 verses.
So the LORD our God delivered into our hands Og also, the king of Bashan, and all his people: and we smote him until none was left to him remaining. And we took all his cities at that time, there was not a city which we took not from them, threescore cities, all the region of Argob, the kingdom of Og in Bashan. ... And we utterly destroyed them, as we did unto Sihon king of Heshbon, utterly destroying the men, women, and children, of every city. Deuteronomy 3:3-6
(The story is also told in Numbers 21:33-35)
Although God is proud of all of his killings, he is especially proud of killing King Og and his people, since they were the last of the giants. Og, for example, had a bed that was 13.5 feet long!
For only Og king of Bashan remained of the remnant of giants; behold his bedstead ... nine cubits was the length thereof, and four cubits the breadth of it, after the cubit of a man. 3.11
Here's what Moses says when he's encouraging Joshua to carry on God's killing tradition.
Thine eyes have seen all that the LORD your God hath done unto these two kings: so shall the LORD do unto all the kingdoms whither thou passest. Ye shall not fear them: for the LORD your God he shall fight for you ... For what God is there in heaven or in earth, that can do according to thy works, and according to thy might? 3:21-24
And Moses has a point here. What other god has killed as many as the God of the Bible?
(Since the Israelites killed everyone in 60 cities, I put the death toll at 60,000.)