Play Left 4 Dead 2 as Bloodhound, Rampart, Revenant and Octane with their full Apex kits and guns.
How to join In Campaign, the host picks "Play With Friends" > "Create New Campaign Lobby", sets "Server Type" to "Local Server", picks "Create Lobby" and invites friends; they accept the Steam invite. Everyone playing needs this mashup from Melty.
Left 4 Dead 2's campaigns, played as an Apex Legends squad.
Pick your Legend on a real Apex select screen, then fight through every campaign as Bloodhound, Rampart, Revenant or Octane - bots take the rest of the squad, and friends who drop in take over a bot's Legend.
Full kits
Apex arsenal: R-301, Flatline, Spitfire, R-99, Peacekeeper and Wingman replace every Left 4 Dead 2 gun, with Apex stats. Shield Cells (pills) give 25 shield; Syringes (medkits) heal 50. Squad HUD with shields, tactical and ultimate, plus captioned Apex voice lines.
Your own Apex install: nothing from Apex Legends ships with this mod. Before the first launch, Melty runs the bundled converter, which builds the Legends, guns, portraits and English text from your own Apex Legends files (takes about 4 minutes, once). Apex Legends itself is never modified.
Converter built from RSX (AGPL-3.0) and ooz (GPL-3.0); source included. Fan-made, not affiliated with EA, Respawn or Valve.