>>14748721A cheap way to balance an encounter is to add friendly NPC's and use more enemies than you think the PC's can take. Like, aim high on the CR. If the PC's are doing too well, the NPC's are getting their asses kicked and need help. If the PC's are fine, the NPC's are fine too (or let the PC's help them finish theirs off.) If the PC's are doing poorly the NPC's can help them. The players don't know how strong the NPC's or enemies are, so they won't know what you're doing.
Just make sure the PC's are the heroes. An NPC gets cut down and is TOTALLY about to die, the healer gets to save him. Healer feels special. Let the others 'lure the bad guys away,' that sort of thing. It's an easy way to add some pizzazz and drama to a random encounter, and it lets you make it seem dangerous without killing any PC's.
Another 'trick' is to adjust stats on the fly. It's not something you should make a habit of, but until you're used to balancing it can help. Say you decided the orc boss had 50 hp. Well then somebody gets lucky on round one and does 50 damage. Obviously you underestimated them, so just say he had 100 HP. Rewrite it to what it should have been in the first place. Don't tell the players, of course.
The same thing goes the other way. Your monster hits the wizard for waaay too much, you pull the blow. Know their AC's and HP's before a battle, always.
Oh and remember, PC's love 'aha! we're smart!' moments. Let's say you know the wizard likes Melf's Acid Arrow. So you can throw Trolls at them, knowing the acid will work perfectly. That way when it happens you say "you seem to recall that a troll's regenerative powers can be stopped by certain magic!" Wizard feels special, the others finish the thing off.
