...not as strange as some of the changes Jimmy Olsen would go through later in his life, but still, a quick look back at some of the earliest with cover art by Curt Swan and George Klein.
Action Comics #253
Jimmy goes to the Fortress of Solitude with Superman, and while there, seem to gain super powers like Superman's! The two end up battling in Metropolis, causing destruction as they fight, with Jimmy using a Kryptonite meteor to force Superman to take him back to the Fortress, where Jimmy tries to destroy the bottle city of Kandor....but Superman stops him, since the Kryptonite meteor was fake (and didn't harm Superman). Superman then frees the real Jimmy from Kandor, as it was look-a-like El Gar-Kur who had taken Jimmy's place and fought Superman.
Superman's Pal, Jimmy Olsen #31
Superman, returning from an outer space mission with a treasure chest, which Jimmy opens, finding a green liquid. Thinking the liquid to be Kryptonite, Jimmy tries to get rid of it to keep his pal safe, but ends up spilling it on himself, giving the photographer the power to stretch....and the lad joins a freak show while waiting for a cure. Along the way, Jimmy gets involved with criminals who want to take out Superman with Kryptonite, but the Elastic Lad stops them....at the cost of his own powers (as the formula inside him seemed to not like Kryptonite).
But don't worry, Elastic Lad would return!
Superman's Pal, Jimmy Olsen #32
Jovians (people from Jupiter) contact Jimmy for help with an experiment...in which they turn Jimmy into one of them...green, scaly and with telepathic powers! This allows Jimmy to get scoops, and even find out Superman's identity....at least for a little while, as the change in race for Jimmy only lasted for a little while. Superman then had to convince the lad that Clark Kent was not Superman!
Superman's Pal, Jimmy Olsen #32 (October, 1958) also provided "The Super Nose For News", by Otto Binder, Curt Swan and Ray Burnley....
....where Jimmy falls victim to one of Professor Potter's serums, which makes his nose grow like Pinocchio's whenever the lad tells a lie. Stuck like this while Potter takes the time to make an antidote, Jimmy gets into trouble only his pal, Superman, can get him out of. Lois gets her hands on the formula, and uses it on Clark Kent, whose nose grows (also disproving Lois' suspicions of Clark being Superman, for now). Superman faked the nose growth in his alter ego, and uses his super speed to more quickly whip up an antidote for Jimmy.
Superman's Pal, Jimmy Olsen #38
Jimmy got the job as Phanto, the old horror TV host, got hurt on set, and needed a replacement for a time. As Neslo, Jimmy did a good job....too good in fact, as a viewer a night started to die from shock. Concerned for his viewers, Jimmy quits the job, but finds out from Superman that the "deaths" were really a government operation, wherein secret service agents' deaths were faked in order to allow them to take on new identities and escape foreign spies.
Superman's Pal, Jimmy Olsen #28
Having a toothache, Jimmy goes to Professor Potter for a cure....but it turns Jimmy into a giant instead! To confound the problem, Jimmy gets a blow to the head, giving him amnesia, leading Superman to chase Jimmy through Metropolis to stop the lad's rampage. Superman does cure Jimmy, but only after pulling his tooth (the pain likely causing his anger), leaving a giant tooth behind.
Superman's Pal, Jimmy Olsen #33
In Professor Potter's lab, Jimmy accidentally breathes a gas which gives the boy flame breath...one would think Superman would keep Jimmy away from the Professor by this time.
Crooks look to take advantage of this ability, using Jimmy to melt through vaults....at least until Jimmy uses the power to create smoke signals for Superman, who stop the crooks as Jimmy's power burns out.
Superman's Pal, Jimmy Olsen #30
Superman appeals to the court to become an adoptive father to Jimmy, which is giving a trial period of 30 days. Things go well, until Superman finds a prophecy that he will end up destroying his son. To save Jimmy, Superman goes out of his way to cause the adoption to fail...much to the chagrin of Jimmy. Superman explains his reasoning to Jimmy, but later finds out the prophecy was about the "sun" of Superman...an artificial star Superman created in another solar system, and not his "son".
Superman's Pal, Jimmy Olsen #38
Jimmy goes to the dentist because of tooth pain (better than going to Professor Potter), breaking a date with Lucy Lane. While there getting tooth repair, Jimmy drifts off to sleep and dreams of a life where he is married to Lucy Lane, though she forces him to end his friendship with Superman before she would marry him. Jimmy and Lucy have Jimmy, Jr., who eventually becomes Superman's new pal, and Lucy learns to accept Superman after he saves the family. Jimmy then wakes up, and meets with Lucy, but is hesitant to set up another date after his dream.
....but Jimmy also had collections that were a part of his own magazine run, one of which featured even stranger transformations!