Get a Gyrm Greatshield (drops from those Gyrm warriors in Doors of Pharros), upgrade it (mine was at +9). It requires 32 strength and has 100% physical and fire block. The Ancient Dragon's fire breath has two ticks of damage, but the Gyrm Greatshield can tank both (assuming you have a decent amount of stamina... I have about 20 endurance I think, with the Third Dragon Ring equipped for extra stamina). Your stamina is completely drained after that, though. So the best thing is to stay in front of it and bait its frontal breath attack, then wail on its front paw or even its head. I used a large club+10 with gold pine resin. Make sure to keep some stamina to not be too wide open. Once it takes off, make sure your stamina is full and then block the fire. If you're badly positioned and the dragon is directly above you, you'll get hit, but for 95% of the time you'll be fine. Rinse repeat, and you can easily perfect him. Way easier than dodging the fire, which requires some luck in terms of how the dragon is positioned.

Darklurker

memory

the war involving the giants though

Plus the timing was annoying. And the giants were awesome good new enemy types... they should have done more there.

Infuse the Rebel Greatshield (it was upgraded at +7 or so, IIRC) with Dark. It barely loses % on other elements but will now block Dark damage at 100%. The Darklurker's damage is all Dark except for those fireballs (which are easy to dodge by strafing/rolling sideways). You can tank every other hit with that shield. Buff your weapon with fire resin (or a spell if you have any magic/faith buffs). He'll split at about 40% normally, so if you can get as much damage as possible for that time period it'll be easier because like the 4 Kings, you don't want to be stuck with two of them at once, at least not for long.

After he split, it's hit and run. In my case most of my stamina was spent blocking and the Large Club, while it its hard, was risky, so... I threw black firebombs at it. It does about 115 damage each. Not that good BUT he doesn't have that much HP, so by playing defensively and carefully chucking those firebombs (and some melee hits if I had a clear opportunity) I managed to take it down on my second try. The shield made ALL the difference. On my first try I got completely overwhelmed.

It would have helped if I knew how awesome Flame Swathe was. I guess he's weak to fire? That and fire orbs were doing big damage. I also have enough VIT and rings that let me run around with a Greatsword easily now so that helped.

Wasted several human effigies beforehand though...

sex-changing coffin. I had no clue what in the fuck that was, and I got in and out of it thinking 'huh, wonder what that was supposed to do', but didn't want to look it up in the event that maybe it would unveil itself sooner or later. Eventually I forgot all about it, and didn't notice any difference because I pretty much never discard my character's helmet. I was all the way over in The Gutter by the time I had to take off my armour to avoid it breaking in that equipment-degrading substance pool, and even then, it didn't hit me immediately. At first, I was like 'I didn't realise just how bulked up the female character could be-- good on Dark Souls for actually including female avatars with physiques easily comparable to those of the males!' Then, once I was done exalting this great feminist achievement for all of about two seconds, I realised she wasn't wearing that strip of cloth that one supposes is meant to be a bra. Now, dodging the whole 'waif-thin female avatars in video games' thing I could buy, but I rather doubted the creators of Dark Souls 2 were making some sort of progressive statement on society's double standards with regards to nudity of the upper body, nor did I think I had chosen a build so muscular the designers figured 'fuck it, her pecs are so developed it's not like she really has boobs to cover anyway'. At that point, finally, it hit me that I'd been playing as a male character the whole time, at which point I looked up 'what the fuck is this shit' and realised the designers had included a sex change coffin that I had obliviously stumbled into.

Interesting little feature. Can't deny I was a bit disappointed to get back into the coffin and come back out so much tinier in comparison, though. 'Great feminist achievement', not so much, I guess. :v

Ornstein is also up there, if only because I'm a big fan of those kinds of little cameos and continuity nods.