As you can see Pennywise isn't human ( lol duh ) They kept his shape-shifting the same in both films. He shapeshifts into kids fears for him to make them more scared and for him to smell their fear.

Henry Power's gang originally had 2 other boys with him in the 1990 version and both of them die but we don't fully see how. In 2017 we see 3 boys with him and see 1 of them die in the sewer.

In 1990, Ben actually meets bill and Eddie at the baron's after he has an encounter with Henry. In 2017 he meets Bill, Eddie, Stan and Richie at the sewer after running from Henry and his gang.

Eddie actually kills pennywise by his inhaler in the 1990 version to help Stan from Pennywise.

In the original Richie actually has a fear of werewolves, not clowns.

Near the end of the 2017 version, you see Henry kill his dad because he was getting told to "kill him and kill them all" But in the original, we see him in 40's and locked away which is when Pennywise makes a return and telling Henry to go back to Derry to kill them all.

One of loser club members does sadly pass away by taking his own life in the original because he gets a call from Mike saying "IT'S back".

Ben actually meets Beverly in his tutor room, but they meet properly after school. In 2017, he says they meet in social studies.

It's actually mike that has an interest in the Derry history because of his dad's photo album of the old iron works. But in the 2017 version, we see it's Ben that has a love for the Derry history

Beverly's dad: In the original, Ben actually leaves the poem outside her front door so she has to receive it but when her dad finds out he actually slaps her which causes her to run away and Ben finds her. In 2017, She pretty much defends herself by knocking him on conscious.

In 2017 we see Bill and Beverly kiss, But sadly in the original Bill gets married and Beverly get's with Ben in the end but before Ben, she was in an abusive relationship.

Stan is actually a bird watcher in the original and if he ever got scared he would hold his ear and call out the list of birds he has seen.

In the original part 2, another loser club member passes away because of Henry Powers.

In 2017, Richie says Bill and Bev kissed for a school performance but in the original, they have no interest in each other. She gets fully introduced to Bill and Eddie because of Ben at the barons.

1990: We see the losers club defeat pennywise in the sewer. 2017: we see them defeat him in the crack head house at first and the second time was in the sewer.

In the original, it is believed Bil's stuttering got worse after Georgie passed away.

The book: after pennywise murders Georgie it was the neighbour that found his body losing a lot of blood and took him to the hospital, but sadly they got there too late. Another point from the book, there's an orgy scene where Bev apparently has sex with the boys from the loser's club.

In the original Eddie's medicine isn't bullshit but the chemist thinks he's lying about having asthma.

In the original Eddie doesn't break his wrist