Edit in JSFiddle

var phyAttackSuffixes = [
"Slam",
"Punch",
"Kick"
];

var spAttackSuffixes = [
"Beam",
"Bolt",
"Blast"
];

var elePrefixes = [
["Flame","Fire","Lava"],
["Water","Aqua","Hydro"],
["Electro","Spark","Thunder"]
];

function getRandInt(min, max) {
    return Math.floor(Math.random() * (max - min + 1)) + min;
}

function getRandBool(){
        return Math.random()<.5; // Readable, succint
    }

function generateAttack()
{
	var phy = getRandBool();
  
  var prefix = "";
  var suffix = "";
  var index = 0;
  var index2 = 0;
  if(phy)
  {
  	index = getRandInt(0,phyAttackSuffixes.length-1);
    suffix = phyAttackSuffixes[index];
  }
  else
  {
  	index = getRandInt(0,spAttackSuffixes.length-1);
    suffix = spAttackSuffixes[index];
  }
  
  index = getRandInt(0,2);
  index2 = getRandInt(0,2);
  prefix = elePrefixes[index][index2];
  
  return prefix+suffix;
}

alert(generateAttack());

//document.write(result1);
//document.write('<br>');
//document.write(result2);
//document.write('<br>');
//document.write(result3);