Connections

Both movies have a scene where the main character is shown a lot of guns by a black market dealer, and he decides to buy all of them.

SPOILERS AHEAD! Both movies end with someone who survived the rest of the movie visiting a gravesite of the movie's killer and being attacked by a hand rising up from it.

Both movies have a character named Tramer and a serial killer that is located in Haddonfield

a murdered man returns from the dead dressed as a scarecrow to have revenge on his murderers

SPOILERS AHEAD! Both have an attempt to kill the movie's slasher on the night of Halloween by filling a room with flammable gas and igniting a cigarette lighter, causing a big fire. It is unsuccessful, as evidenced by a sequel.