actually, try this:
command /create [<text>] [<integer>]:
permission: skript.create
permission message: "&c&lHey! &r&4Sorry, but you can't use this command."
trigger:
if arg-1 is not set:
send "&c&l[&4&lError&c&l] &r&4Mob is not set."
else if arg-1 is "Mobs":
send "&cMobs: Cow, Pig"
else if arg-1 is "Cow":
if arg-2 is not set:
send "&c&l[&4&lError&c&l] &r&4Set the amount of mobs you wish to summon"
else:
summon arg 2 cows at location at player's targeted block