I've never had to drastically change up my build for a boss, but I'm shaking everything up to fight Radahn. Going for the tankiest build possible.
From head to toe, and spell to weapon, I'm tailoring every aspect of my build exclusively for this bastard.
Not since my first playthrough of Dark Souls 1, where I fat rolled in Havel's armor just to beat Nito, did I focus so much on one boss. I'd later be able to beat him and everyone else just sporting a loin cloth to roll better. Radahn is a different beast.
I'm going with the best holy damage negation gear and focusing on stamina/shield for practically everything else. It's taken me on a crazy journey through parts of the base game and DLC I missed. It's probably a good 5 to 8 hours worth. It's been a lot of fun!
I'm still undecided on my weapon. I want to finish him off with my Claymore, but might need a faster poke weapon. Any suggestions?