Okay, I got it.

For Samus' suit, it's up-down-up REALLY FAST

For the Snake and Star Fox calls, it's down for ONE FRAME, you hold it any longer and you get the taunt. And if Snake, Fox, Falco or Wolf kneel and then get hit before the call comes through, you can't do it again, so make it count.

I'll have to try those. I did get Falco to do a call once before on the Coneria stage, but that's it.

For some reason now, I can get Snake's calls with no problems. Usually he only taunts once and then does it, I usually just hold my left thumb on the up button with good force and press the bottom D-Pad with my right thumb as fast as I can, and when that goes down the up d-pad button probably will too.