The Cardinals came in first place, just 2 games ahead of the Giants. The Giants were only one game out going into the final day of the season. Dean won a complete game on that day.
Dean was outstanding the last two months of the season. In August, his ERA was 1.41 in 51 IP (46H, 33K, 10BB, 2 HR).
In September, his ERA was 1.54 in 64.1 IP (45H, 41K, 16BB, 3HR). He started 7 games, completing 6 AND he pitched 5 games in relief (for the whole season, he started 33 games and pitched 17 in relief).
In the last 6 days of the season, he pitched 3 complete games, allowing just a total of 2 earned runs (one game was on 2 days rest and the other was on 1 day of rest!!). In those three games, he had 20H, 19K, 3BB, 1HR. He won all three games.
He saved 2 games in September (he had a total of 7 saves that year with a 4-2 record as a reliever). On September 11, he had a 2.1 IP save the day after pitching a complete game. He also pitched one-third of an inning on September 12.
He did have a gap of 12 days when he did not pitch at all, from August 12-August 24. He had a 10 day suspension. For details, see A Closer Look: Dizzy Dean Wins 30 in 1934 by Gabriel Schechter. There was also a victory awarded to him in a questionable decision by the official scorer. Otherwise, he wins only 29.
Twice he pitched 3 innings in relief the day after pitching 9 innings. Another time it was 2.1 IP the day after pitching 9 innings. Still another time it was 2 IP the day after pitching 8 innings. In all, he pitched in relief six times the day after starting and going at least 8 innings.
He also pitched in relief in both ends of a double header on September 23rd, after a complete game on Sept. 21. Then he pitched a complete game on Sept. 25 followed by CGs on Sept. 28 & Sept. 30!
The he started game 1 of the World Series on October 3, on just 2 days rest and got a complete game victory. His next start was Oct. 7. He lost in 8 IP, but it was still a complete game. He then started game 7 on October 9, on only one day of rest. He pitched a complete game shut out against a lineup that included the following Hall of Famers:
So he had 6 starts in a 15 day stretch and completed all of them. He allowed only 5 earned runs in 26 IP in the World Series.
From Baseball Reference:
Dean's 1934 splits
Dean's 1934 game logs
Dean's post season game logs