Warped Polygon | RetroArch | 2 Player Mouse Easy Setup Guide @warpedpolygon | Uploaded December 2022 | Updated October 2024, 11 hours ago.
DISCLAIMER: Footage captured with Model 2 EMU because you can remove the screen flash. I opted for this for obvious reasons. However there is a 5 second part in the video with screen flash to demonstrate that the method works. It will be signposted and timestamped here

Screen Flash at 4:58

COPY AND PASTE WHAT IS BELOW:

input_driver = "raw"
input_max_users = "2"

input_player1_mouse_index = "0"

input_player1_gun_trigger_mbtn = "1"
input_player1_gun_offscreen_shot_mbtn = "2"
input_player1_gun_aux_a_mbtn = "3"
input_player1_gun_start = "num1"
input_player1_gun_select = "num3"
input_player1_gun_aux_b = "num5"
input_player1_gun_aux_c = "num6"
input_player1_gun_dpad_up = "up"
input_player1_gun_dpad_down = "down"
input_player1_gun_dpad_left = "left"
input_player1_gun_dpad_right = "right"

input_player2_mouse_index = "1"

input_player2_gun_trigger_mbtn = "1"
input_player2_gun_offscreen_shot_mbtn = "2"
input_player2_gun_aux_a_mbtn = "3"
input_player2_gun_start = "num2"
input_player2_gun_select = "num4"
input_player2_gun_aux_b = "num7"
input_player2_gun_aux_c = "num8"
input_player2_gun_dpad_up = "w"
input_player2_gun_dpad_down = "s"
input_player2_gun_dpad_left = "a"
input_player2_gun_dpad_right = "d"