Can someone explain to me an easy way to advance monsters. I'm wanting to take "run-of-the-mill" creatures. . .goblins, kobolds, lizardmen, etc. anf make them more of a challenge for higher lvl pcs (lvl 8+) and I am not sure what I need to do.
Any help would be great!
The easiest way is to just give them class levels. And actually, I'm pretty sure that's the only way to do it for your example creatures.
Me, I would just use ogre magi, stone giants, or efreeti. Or many hill giants or even many more trolls. Or a smaller number of advanced trolls.
But if you must use puny monsters advanced enough to make them challenging at CR 8, then you have very few options. Even an Advanced Giant Fiendish Goblin is still not a CR 4 monster. If you put about 10 of those into a single encounter, it would be about CR 8, but even then, you should give them an edge, like an ambush, or terrain features, or some traps they set up, or something to give them a chance or they'll die fast.
Racial HD might do the trick, but really, those are for monsters. And I don't mean monstrous humanoids. I'm talking aberrations and beasts and magical beasts, or maybe even elementals or outsiders too.
Which only leaves class levels, as knightofstyx already pointed out.
Really, you're asking the same question as "I want to challenge 8th level characters by having them fight evil humans. How can I do it?" The answer is the same, anyway.
Isn't there a program online that you can use to make characters/monsters with lvl? Can't remember the name.
The easiest way is to just give them class levels. And actually, I'm pretty sure that's the only way to do it for your example creatures.
That's definitely right for Goblins and Kobolds, Lizardfolk do have racial HD though so not sure on them, though I personally would just give them class levels too.
I've seen a few folks use this:
http://www.wolflair.com/index.php?context=hero_lab&page=pathfinder_role playing_game
Lizardfolk go great no matter how you advance them. Large, or even huge lizardfolk, half-dragon, half-fiend, and just about every class works well. I would say that gnolls, bugbear and others are a better off being advanced with class levels rather then HD.
When in doubt, just do a half-assed quicky upgrade:
5 levels of class gives BAB/saves, and a few special abilities - such as a few combat feats, sneak attack progression and evasion, spells, channel energy, smite, weapon and armor proficiencies, etc. but skip domains, school specializations, bloodlines, trapfinding, etc.
Lie. Use the stats for, say, minotaur, and learn to describe it to your players as 'elite goblin soldier'.
You could always use this too.
If it could class levels it would be supremely awesome. This way it's still awesome though. I could really use it because I wanted to create a small army of various half dragons.
Lie. Use the stats for, say, minotaur, and learn to describe it to your players as 'elite goblin soldier'.
This.
The fast templates in the Bestiary are good too.
Honestly though, the GM is not under any obligation to "play by the rules" of monster generation. If "fairness" is an issue, observing CR should be sufficient (although I don't fret too much over CR myself).
If the players are capable of fighting a CR4 minotaur and they end up fighting an ogre (CR3) who is actually statted as a minotaur, and you award CR4 xp, I see no problem.
The realization that the players couldn't actually "see" the statblock was one of the best moments of insight I've ever had as a GM.