Your first character must be Sent or Wolvie to fight him. However with wolvie you can use your second partner(Anyone).

i have beat onsluaght many times this is how you do it...
one of your character has to be sen. cyc or ryu use your levels fast and use your varables quickle....

Sen. is the best to use it on onsluaght because you can use rocket punch and those litte sen. :buttrock: