Why fight with clothes?
I can't see any requirement to do this solo, nor that all your party members have to be naked as well.
In which case it would be simple: find a friend (or two or three), join up, and let them kill the boss with their gear. Probably you will die during the fight, but that won't stop you from scoring achievements.
I haven't tried this out yet, so this is pure speculation.
Update: yx. has tried it, and confirms it works (see comments). Thanks!
I did the Cydaea achievement solo on a Demon hunter, and it is about as annoying as you'd imagine. First off, you only need to take off your gear at the end (obviously). Here's how I did it:
Take a decently geared DPS companion. Mine was at ~500 DPS.
Fight like normal, get her down really low (<10k). Then retreat to the other side of the map.
Start taking off equipment. (Do NOT drop it on the ground.) This is annoying because you have to go into your inventory and you're pretty much blind the entire time, hence the retreating part. If Cydaea enters an add phase (lots of spiders spawning and Cydaea vanishes) don't stand still. You need to move and kill them ASAP.
Keep in mind ANYTHING will oneshot you when you're naked. Smoke Screen really helped me.
Once you're naked and there are no spiders alive, move your companion within range of Cydaea and hope they target her. She will spawn a small amount of adds even outside the adds phase, and she likes to retreat behind them, causing your follower to target them instead.
If Cydaea isn't dead before the next add phase (about ~30 sec between them), put weapon back on and kill the adds while avoiding them. If you don't do this, the adds will pile up fast. When the coast is clear, unequip weapon and move back to Claudia Black.
Rinse repeat
It took me about 15 tries, mainly because spiders can spawn right under you and oneshot you in a heartbeat when you're naked (Keep moving!). It might be easier in coop, with 1 player handling adds/optional ressing, and the other hurting her, but you won't have the follower and your naked DPS is roughly...10.
The other bosses? I haven't tried them yet, but they might actually be easier, because there's no adds, though having to dodge stuff (Belial...) while taking off your gear is probably the trickiest part.
I'm yet to attempt it but a Witch Doctor would be the most obvious solution for these achievements. Using his/her pets to take the brunt of the hits and do DPS can largely be equipment agnostic, as opposed to Barbarians and Demon Hunters for example, who would both significantly suffer if they are unable to equip a weapon.
Select your skills and runes such that they all either boost your summons or your own survivability (since you'll have no armour), and it would give you the best chance out of all the classes to manage this achievement.
I haven't tried to get that achievement yet, but your follower should be able to help you with this.
Here's how I would do it:
- Equip your follower with some decent gear
- Fight the boss with your normal gear until he/she/it is at very low health
- Unequip all items and let your follower finish off the opponent
Warning: Don't drop your gear to the ground. Use your inventory instead! If the boss kills you (which is quite possible since you're not protected by any gear), you'll lose all your items. This is because the boss area will respawn if you enter it again and all your stuff will be gone.
If you're a high level Demon Hunter, start a game and:
- Marked for Death + Death Toll
- Sentry + Spitfire Turret
- Shadow Power + Gloom
- Smoke Screen + Lingering Fog
- Ballistics
- Custom Engineering
- Perfectionist
Then get to the boss, drop a sentry and avoid the boss' attacks until the sentry despawns. Repeat. Also if you try this with Diablo, remember to punch him for another achievement, "Punch Diablo".
It may not be the best DH approach, but the best I can think of with no abilities based on a % of weapon damage.