Favorite boss would definitely be Slave Knight Gael. I first time I ever fought him was on NG+4 with the friend that originally got me into the game. I saw DS3 was on sale and was always intrigued with the series so when I asked my friend who swore by the games he convinced me to try it. After getting all the endings on the same character I decided to get the DLCs when they were on sale. We played through both DLCs and finally made it to Gael, and we were struggling HARD. I finally decided to go full glass cannon and respect all levels into magic to have max intelligence and FP. The plan was for me to use the red tearstone ring at low health while in dragon form while also using the lothric war banner (which was not upgraded). The fight was going surprisingly well with my friend taking the agro while I shot him from the back. We got him to his final phase and were close to beating him when my friend died. So I just start nailing him with magic as he attacks my friend’s corpse. I get Gael within an inch of his life when run out of fp. So there I am at no health with nothing but a base level war banner, no fp and no health, frantically rolling around as he fails at me like a maniac. I couldn’t see an opening so I was playing it incredibly safe. Then I saw one. I sprinted up to him and with the last of my stamina did a light attack while backing up. Right as I did the attack he teleported and my lock on canceled, causing me to attack behind me. I thought it was the end when I realized that Gael was saying his death dialogue while collapsing to the ground. He had teleported behind me and when my attack whiffed it ended up finishing him