However, for Derbyshire Mitchell went from strength to strength in the dry summers of 1933 and 1934, at times bowling with sensational skill, as when he dismissed Worcestershire for 48 on a good pitch in 1934. He was close to the top of the averages in those two seasons, but from the 1935 season appeared to sacrifice length to gain more spin and often suffered heavy punishment. That year, he was offered terms by Lancashire League club Colne, but decided to remain with Derbyshire. Still, he could be deadly on his best days, as when he took all ten wickets in an innings against Leicestershire for 64 runs at Leicester in 1935 or when he took 7 for 26 against Gloucestershire on a blameless pitch at Derby a year later. Mitchell set a record for Derbyshire with 168 wickets in 1935, but in Derbyshire’s Championship win in the 1936 season he was considerably less successful and at times very expensive even when conditions favoured bowlers (e.g. against Kent at Burton-on-Trent and Warwickshire at Edgbaston). Still, on Mitchell's good days Derbyshire's bowling that season could compare with almost any county side in history, and the following two seasons still saw him as one of the best spin bowlers in England. In the 1939 season, however, Mitchell did not do much work because Derbyshire's pace attack was so consistently effective and he failed to take 100 wickets for the first time in eleven seasons. During World War II Mitchell played for Lidget Green in the Bradford League, but when he refused to rejoin Derbyshire due to his engagements in League cricket, the Derbyshire committee declined to give Mitchell the benefit he had been due to receive in 1940. He did, though, continue to baffle batsmen for Hickleton Main well into his fifties. At his best a master of flight and variety, Mitchell was capable of many more balls than the typical leg-break and googly bowler, perhaps because he learned his art in an unusual way from spinning a billiard ball. Often he would vary his leg-breaks with off-breaks made by turning the wrist in the opposite direction to that of a conventional leg-break or googly, and his top-spinner also brought him many wickets. However, Mitchell, unlike such bowlers as Tich Freeman, was erratic and, especially in his later years, he could have days where he was heaven for batsmen wishing for quick runs.