Making challenging and memorable bosses

[Silva Stormrage]

Hello, my first camphain is coming to a close and looking back on previous bosses I realized that maybe once I have acuratetly judged what the player's reaction and difficulty overcoming the boss would be. The bosses I think are going to be challenging are either a push over or trivilized by something I didn't expect (an ability to push everything back in a 100ft radius to the edge of the radius agianst a huge horde of ghouls for example). And the ones I think are going to be easy but not pushovers seem to take the players ages to kill and get them incredibly nervous and close to death.
I think in the entierty of my campaign there has been one boss that has been challenging that wasn't just one shot. It doesn't help that my players enjoy rocket tag and previously thought optimization meant glass cannon :smallsigh:.
So is this just something that comes with more experience? I don't seem to have any solutions to making boss encounters more difficult without them just slaughtering the party. I've tried adding extra creatures to act as giant meat shields but the party generally damages them along with the main boss at the same time with large AOE's. Just increasing the boss's health doesn't work because they use save or dies all the time. Any tips would be appreciated and I will probably try to tweak the remaining few boss fights accordingly.

My players for reference:
Druid/Sorc
Spell Thief
Cleric

[AslanCross]

I'm always an advocate of using the terrain to the boss's advantage. The boss should fight on his own terms, such that even if the PCs try to attack him in his bedroom, there's a whole bunch of dirty tricks the boss can pull off that the PCs can't expect even if they know what the boss does mechanically.

It can be something as simple as having the boss on a platform 20 feet above the PCs. It could be a bit more complex, like having a chain devil fight inside a magically cold slaughterhouse---the cold damages the PCs, but the devil is immune to cold. The chain devil can use the meat chains to attack from different directions, as well as pretty much spider-climbing across them. The numerous hanging carcasses could provide cover as well.

It could be something as difficult as a beholder inside a library wherein the shelves are mounted on sliding rails, such that they not only provide cover but can be telekinetically pushed by the beholder in a certain direction.

Throwing a blue dragon at the PCs? How about on a treacherous hanging bridge over a quarter-mile-wide chasm during a thunderstorm?

Sometimes it might not be mechanical advantages: Sometimes it's simply atmosphere. The final battle in the Siege of Brindol in Red Hand of Doom has the hobgoblin general storming the cathedral square with a cadre of giants under the blare of dragonbone horns. In my campaign, the PCs had taken all their NPC underlings and mounted them in the square's grandstand, while the PC sniper and the NPC he trained hid up in the cathedral's spire.

The general comes in with his elite guard, and not only trumpets his entrance with horns, but by launching a fireball (via necklace of fireballs) at the giant holy symbol of the cathedral, setting it on fire. The bright illumination in the encounter came from the burning symbol.

Sometimes, this does backfire: I devoted a lot of effort into improving the black dragon boss and his goblin ranger rider in the first half of the campaign, but due to stupidity on my part they pretty much blew it out of the sky as it flew towards their hiding place. I completely forgot that the dragon had water breathing and its rider could hold his breath for several rounds---at least long enough to approach the PCs from the sunken staircase in their bell tower from below.

[Antonok]

a boss I particularly liked that I threw at a party I was GMing for looked like just a normal giant montrous spider, but it about TPK'd the party. I knew the party didn't have any darkvision (and that they only had 1 torch among them) so I put them in a 20ft high 40 by 40ft room that went completely dark when they triggered the boss fight. The boss had a bite attack that could either paralyze or inflict a reverse gravity effect, so I used the reverse gravity effect to put the rogue (only one with a ranged attack, boss had a high Int score) on the cieling so the boss could knock him unconcious, then did the same thing with another char except when he was on the cieling I used the bosses paralyzing effect then dismissed the reverse gravity so it made that char fall knocking him unconcious, and finally the last char standing decided to stand on an alter that was in the middle of the room and took a ready action to attack it (he was a warforged DrNecro) and finally killed it. It was probably the most stratigic boss fight I've ever thought of and it was a rly good fight.

[Chilingsworth]

If your players are hitting your henchmen with AoE's. then give those henchmen evasion and decent reflex saves. If they are using save or die spells, give your big bad better saves and Deathward. A couple levels of rogue on the henchmen will take care of the first problem. Either an item of deathward, or 7+ cleric levels will take care of the death spells for the second.

[Scarlet-Devil]

Depending on the PCs levels, something as simple as a belt of spell resistance could have a major effect on the difficulty for them, considering you've got a party of casters. A minor cloak of displacement could be very effective too, both for evading spells and rendering him impervious to sneak attacks. A lot of demon/devils come with awesome resistances/damage reduction right out of the box; something like an assassin devil with some class levels and magic items could be quite devastating, particularly if the devil tries to fight them in magical darkness (which only he could see through, in all likelihood).

Edit: Yes, I think a Dogai(FC2) would be an excellent challenge for these guys, assuming you want to give them a kick in the pants, as my old DM would say they deserved for killing bosses with save-or-dies.