Crash Commando

First of all, pay attention to the fact that bots won't work for this, it must be against four (or more) human players. That also means it can only be obtained online. (Click here for the boosting thread)

You don't have much time between kills, so make sure you are comfortable with firing your primary weapon, any explosives and the death spin before attempting this. This will nearly never happen in a normal game, as the other players would kill each other too. Even when you get a high combo, it is often not from using each of these once. Some people have a hard time getting this even with boosting partners, but simply be calm for the five seconds it takes to combo, and you'll be fine.

I strongly suggest you boost this in a five player death match session with four other HUMAN players (no bots). Obviously you need to choose the explosives before you spawn (I suggest grenades), and pick a real weapon (basically anything other than the CAB healing ray - a machine gun will work fine).

Before you can death spin, you need to first build up your special by killing enemies till the icons on the bottom of the screen glow, then hit to select the fire circle on the right.

Now have all four boosters stand in an orderly fashion, and make sure they understand what each person's role is over the five second madness. You want to have the booster closest to you jump, throw the explosives at the two boosters behind him (they should quickly run on top of the explosives so it will kill them when it detonates), then quickly death spin into the booster that jumped, and fire away with your primary weapon to kill the one or two remaining boosters that didn't die from the explosives.