There comes a time in every DMs campaign when they realize that they did not prepare for an encounter. They then realize that they have this entire body of suitable monsters that they have created to face the party, but they have names and descriptions that don't match up for what should be where they are. So the DM changes the name and look to match what he wants but the mechanics are from previously encountered foes. Most players won't notice unless you're giving descriptions such as "like the goblins from before only red" or "A troll covered in blue moss instead of the usual green". Most players aren't in the caring camp either. As long as its not a TPK they've got fun stuff to do. At least until it gets out of hand. Then the players notice that you've not made a different monster mechanically for over a month and all the monsters seem to be color variants of the ones they've been fighting for the past many sessions. To sum up. Use refluffing sparingly or your players may get wise to your tricks.
Art from GIS for Dragon Warrior Monster