Goofs

(at around 2 mins) When Deadpool is laying on the drums of fuel, he's wearing blue Crocs. When Colossus comes to the apartment to retrieve him from the rubble (at around 21 mins), his feet and legs are shown in his black boots.

When Juggernaut causes the bus to crash, Deadpool loses one of his guns which Cable grabs out of the air. But after the crash, when Deadpool wakes up, both of his guns are in their holsters.

(at around 1h 2 mins) After getting caught on the billboard, Deadpool releases his parachute from its harness and lands on the billboard's catwalk. The parachute's straps can be seen dangling behind Deadpool's head in the following closeups. In the long shots, the parachute is nowhere to be seen.

The dent in Colossus's head disappears and reappears between shots.

In the opening scene, Deadpool turns all the stove dials counterclockwise (presumably to turn on the gas). A moment later as Deadpool is standing in front of the stove, the dials are mostly back up at the 12 o'clock position.

(at around 1h 8 mins) When the brakes on the prison rig are cut, they leak hydraulic fluid making it unable to stop. A vehicle of that size and weight would definitely require air brakes, which not only don't leak fluid but apply automatically if the fluid line is cut.

(at around 1h 1 min) When X-Force deploys their parachutes, they all shoot upwards. In reality, this does not happen, it's due to a common misconception from watching footage of skydivers: when a skydiver opens his chute, he merely slows down, but when he is being filmed by a cameraman who is still in free fall, the relative motion makes it appear as if he's going upwards.

None of Russell's clothing ever burns or catches fire even though his hands are supposed to be hundreds or thousands of degrees.

(at around 2h 5 mins) [Super Duper Cut only] When Deadpool uses Cable's repaired time travel device at the end, he goes into an Austrian maternity hospital in 1889 to kill a newborn Adolf Hitler. Hitler was born in the home of his parents, not in a hospital.

No matter how super-strong a person might be, a long, heavy vehicle cannot be swung around by grabbing onto its front end. Without being braced against a fixed backstop, they only would move themselves around instead, and even if they were so braced, then all they'd achieve is severe damage to the vehicle's front end.

(at around 2 mins) At the beginning of the film, Deadpool says he was on top of 1,200 gallons of gasoline. In fact, he laid on seven 55-gallon drums for a total of only 385 gallons, and several of the drums were labeled as kerosene. However Deadpool tends to exaggerate his statements and was just being dramatic.

(at around 12 mins) Vanessa starts to rotate back when the bullet is clearly still in front of her. However, it is very probable that she would have tried to turn around to run away, though she most likely wouldn't have been able to avoid the bullet.

When Deadpool kills Ryan Reynolds, it is supposed to be before he has filmed Green Lantern in 2011 and unmarried. However, while he's reading the script, you can see Ryan's ring meaning that it is a present Ryan reading the script. However at the time Ryan Reynolds was still married to Scarlett Johansson in 2010 and wouldn't file for divorce until December of that year. So him wearing a wedding ring isn't a character error.

Time travel, if possible, doesn't allow changes to the past. It allows jumps to different timelines. So Cable's family on the original timeline will always be dead, and changing the past is pointless. It would be far easier to find a reality where Cable is dead and his family is alive.

However, as time travel is not possible, there are no "official rules" on how one can fictionalize the plots of their story-telling. Different timelines are as fictional as changing events in the past.

(at around 33 mins) Wade reacts a few seconds before Colossus grabs him by his neck.

(at around 35 mins) When Deadpool and Firefist are put in jail, the door is closed, and the shadow of someone crosses the bridge, but there is no one on the bridge. Similar shadows with prisoners are seen, but this one is alone.

At the beginning of the movie, Deadpool wipes blood off a security camera lens using his entire hand.

Security camera lenses are tiny and can be cleaned using a finger, not an entire hand.

In the parachute scene, the cars on the road are parked in the opposite direction from the flow of traffic.

The bus that Bedlam crashes into and the car which Peter narrowly avoids are headed in opposite directions on a one way section of street.

If Cable's mission was to stop Russell becoming a serial killer by whatever means, he should have just left him in the inescapable Icebox prison. Wade would have died of his cancer because of his collar so would be of no help. Cable breaking into The Icebox to unnecessarily kill Russell is what leads to everything else that subsequently occurs i.e. Wade regaining his powers+escaping, the Juggernaut+Russell escaping, the death of X-force, and the almost making of Russell into the serial killer Cable was originally trying to eliminate.

Wade says he has a gluten insensitivity, but mentions wine in his explanation. Wine is actually one of the naturally gluten free alcoholic beverages, save for cross-contamination.

When Deadpool and Cable are trying to get through to Russell, Deadpool remarks how difficult it is to get through to Millennials. Russell is too young to be a Millennial. He would be Gen Z.

Deadpool derisively refers to Cable as "John Connor," in reference to Cable's cybernetics resembling those of the titular robotic killers in the Terminator franchise. John Connor was the enemy of the Terminators and fully human, not one of the cyborgs.

When describing himself and Juggernaut as a team, Russell compares the two of them to Tupac Shakur and Ice Cube. Tupac and Ice Cube were not a team. They only recorded one song together ("Last Wordz" from Tupac's album "Strictly 4 My N.I.G.G.A.Z."), on which Ice-T is reported to have worked as an intermediary between his two fellow West Coast legends.

When Wade is giving examples for films where the hero hits rock bottom, he mentions "In 'Cool Runnings', it's when John Candy broke his prized bobsled." This does not accurately describe the plot of the film 'Cool Runnings' (1994), as the bobsled is neither John Candy's nor it is prized but rather a lousy donated sled. It is also not a good example of the hero hitting "rock bottom" as the bobsled breaking happens at the climax of the film instead of midway through the plot.