Corrupted Sentinel

Act: I

Location: Lowlands Monastery

Attack Phases
This boss has a shield, which negates all attack. He will move this shield (if a bit slowly) to block you on either side.

The boss also has two general attack sequences. The charge, and the regular attack. If you are efficient, you will most likely see the charge much more often. Just like all other enemies, the boss' eyes will turn red, and he will slowly raise his weapon before he is about to regular attack. He will also turn a bit red before charging.

Strategies
This boss is the first enemy encounter with a shield. However, he uses his shield quite ineffectively. If you just dash to his other side and jab at him every time he turns his shield towards you, you will get off solid damage.

If you are stubborn, and want to face him head on, you can stun him into dropping his guard, and then attack him, but otherwise stick to the first plan, because it is faster and more efficient.

In order to counter his charges, you are able to see them coming pretty well, so just blip right through him when he begins to slowly run towards you, and he will end up careening into a wall and dropping to the floor. This is the biggest opportunity for damage. When he is stunned on the ground, take as many hits as you can on him, while also using the free time to take care of the enemies that spawned as well. As long as you are constantly dodging and hitting, even a bit blindly throughout this fight, you should be ok.

Rewards
The reward for defeating this boss is a chest containing your first mending flask. This is an incredibly useful item that can now be upgraded further in the trading shop.