The plot of "Mersal" was much similar to Kamal Hassan starrer "Apoorva Sagotharargal". Both of the films have a similar revenge plot where father has been killed and two of his sons return to avenge their father's death.
A scene sequence from "Law Abiding Citizen" where a person was punished by getting suffocated inside a box with medical amenities, was copied in the film "Mersal".
A scene between Danny (Jesse Eisenberg) and Dylan Rhodes (Mark Ruffalo), where Danny trickily snaps his handcuff around Dylan's hands was copied in the film "Mersal".