As the first boss you’ll encounter in the tutorial area of Dark Souls III, Iudex Gundyr doesn’t really put up that much of a fight. After you pull the Coiled Sword out of his body, he’ll begin to rise up. You can take this opportunity to get some free hits in.
Like most other bosses in the game, Iudex Gundyr has two phases to his boss fight. The first phase is relatively straightforward; he’ll swing at you with his halberd, though these are easily dealt with simply by blocking with your shield, or using the i-frames in your dodge roll to get out of harm’s way. In case you’re a little rusty with your dodging, remember to time your dodge and hit the roll button just as the attack is about to hit you. Your invincibility frames will do the rest of the work for you. Iudex Gundyr will also perform a leap attack where he jumps into the air and smashes the ground with his lance. When you see him leap up, roll under him and you’ll be in a perfect position to get more hits in as soon as he lands.
When you get him down to 50% of his health, this is where the real fight begins. The boss will sprout a large, black tentacle out of his head, and he gains considerably more range to all of his attacks. These attacks can still be blocked with a shield, but take note that each blow will deplete a lot more stamina than his regular attacks did. What you want to do during this phase of the fight is stay as close to him as possible because he doesn’t have a lot of close range attacks.
If you chose a starting class with a shield, be sure to keep your shield up when you’re close to him so that you can absorb his attacks. To be safe, you should only go in for hits when he’s using one of his long range moves.
Iudex Gundyr is a pretty straightforward fight overall. He’s slow, and many of his moves are actually punishable. If you’re good with parry timings, a lot of his first phase attacks can be countered with a riposte, and this will quickly make short work of him.