how do i make an item wich when i right click creates a wall in front of me? (reposted)

In the green Event trigger, put "Entity dies" Then put this: "If ['Is Event/target entity (sub)type of Monster entity' AND 'Is Source entity (sub)type of Player]". do "Set score "hostile_mob_kills (or any other name)" to [[Get Source entity scoreboard score for "hostile_mob_kills (that same name)"] + 1] on the scoreboard of Source entity.

When you get in Minecraft, do /scoreboard objectives setdisplay sidebar "your scoreboard name"