So here is a good Question how the hell do you beat that Sleazy Wyvern in Dark Souls 3? well say no more you came to the right place, here is a quick written guide on how to Kill this sleazy Enemy that always makes you crap yourself. Dark Souls 3 Ancient Wyvern Guide
Dark Souls 3 boss: how to beat Ancient Wyvern
You know how we’ve been favouring cheesing and ranged attacks and then coming to bosses and saying “soz, you have to melee now”? Friends, our time has come. Equip your best fire-proof shield and some nice light armour for sprinting, then head through the fog gate.
As you run up these stairs, an Ancient Wyvern descends. Finish shitting your pants and run straight past it; its wings pose no obstacle. Turn left at the top of the stairs and run or roll past the dragon hybrid guarding the door. Turn left again and run past two more dragon hybrids, and when you come to a T junction a moment later, turn right and pause just before the stairs, turning to face any baddies on your tail.
You’re safe from fire breath at the far end of this room, and it usually takes out the dragon hybrids who’ve been chasing you; deal with them if not. Two more dragon hybrids attack as you venture out onto the curving stairs, including one that jumps down as you cross the threshold. You’re safe from fire here, so you can take your time in dealing with them – or more dangerously, just leg it.
At the top you’re still safe from fire so if you lost your followers you might want to fight the dragon hybrid here before another dragon hybrid comes shooting out of the doorway on the left as you advance. Otherwise, again, just keep running.
The bridge ahead is the hardest part; there’s a sniping dragon hybrid behind and above you, and a sniping dragon hybrid and a giant dragon hybrid ahead. Worse, if you venture too close to the bridge the ancient wyvern’s fire breath will melt you. I suggest sniping down the enemies ahead, then sprinting across and rolling if you head the sniper fire at you from behind.
On the other side there’s just one more dragon hybrid, and then you can climb a ladder. Immediately pause with your shield up while the ancient wyvern bathes everything with fire. When it’s done, run along the wooden platform.
From these wooden scaffoldings you can drop down to a stone ledge on your left – it will be marked with messages, even offline. You are out of reach of the breath attack here and can and snipe for your life; the boss takes extra damage from headshots. You can also try plunge attacks if you don’t mind running and repeating; they work very well indeed if you manage to hit the head.
After the battle you’ll receive the Soul of Ancient Wyvern and be transported to a new area. Activate the Dragon-kin Mausoleum bonfire immediately.
This is the best Written guide I found on how to take down that Sleazy dragon impostor, you do get rewarded nicely at the end too so its in your best interest to slay this giant beast. Dark Souls 3 Ancient Wyvern Guide