By "Kill" a character, perform an Ultimate/No Mercy/Stage fatality on the character and then proceed to defeat Gargos.

Ending	How to unlock
Combo Ending 1 & 2	Kill Tusk or let him live.
Fulgore Ending 1	Don't kill Orchid or Jago.
Fulgore Ending 2	Kill Orchid and Jago.
Fulgore Ending 3	Kill Orchid, but bot Jago.
Fulgore Ending 4	Kill Jago, but not Orchid.
Gargos Ending	Just defeat the last boss.
Glacius Ending 1 & 2	Destroy the wall in Sabrewulf's stage and then kill Sabrewulf or let him live.
Glacius Ending 3 & 4	Do not destroy the wall in Sabrewulf's stage, but kill Sabrewulf or let him live.
Jago Ending 1	Don't kill Orchid or Fulgore.
Jago Ending 2	Kill Orchid and Fulgore.
Jago Ending 3	Kill Orchid, but bot Fulgore.
Jago Ending 4	Kill Fulgore, but not Orchid.
Kim Wu Ending 1 & 2	Without using a continue, kill Spinal or let him live.
Kim Wu Ending 3 & 4	Use at least 1 continue and kill Spinal or let him live.
Maya Ending 1 & 2	Kill Tusk or let him live.
Orchid Ending 1	Don't kill Sabrewulf or Jago.
Orchid Ending 2	Kill Sabrewulf and Jago.
Orchid Ending 3	Kill Sabrewulf, but bot Jago.
Orchid Ending 4	Kill Jago, but not Sabrewulf.
Sabrewulf Ending 1 & 2	Kill Glacius or let him live.
Spinal Ending 1 & 2	Kill Kim Wu or let her live.
Tusk Ending 1 & 2	Destroy the hanging piece of wing in Glacius' stage and then kill TJ Combo or let him live.
Tusk Ending 3 & 4	Do not destroy the hanging piece of wing in Glacius' stage, but kill TJ Combo or let him live.