First is the ability to harden, which essentially replaces the ability to block. Using harden can be a very good tactic in battle and will turn your shell into stone for a brief time to deflect enemy attacks. This does have a cooldown window after use, but it can be activated any time; during a dodge, mid weapon swing, or whilst just standing still. This opens up new ways to defeat your enemies in combination with the parry ability that can be acquired within the world.
There are no Estus Flasks in Mortal Shell, so to say, there is no permanent item that will replenish your health. There are some items scattered across the world that you can collect to provide different benefits like faster regeneration of stamina or health, or other buffs like poison attacks. But your main method of replenishing your health will be using the aforementioned parry feature. Each shell has a resolve limit (up to 5 bars), which can be built up during combat, and with each full bar, you can follow up a successful parry with an attack that will drain the health of your enemy and place it into your own HP bar.
An interesting component to the various items you can collect and use is that each item will have its traits hidden until the first time you use it, so you won’t know what a new item does until you actually utilise it. Further to this, the more you use an item, the more familiar your character becomes with it enabling an extra effect and understanding of these items. Some items in the world also have a respawn rate, so you can return to this spot after a set amount of time to collect the item once again.