An IPotionEffect is an IPotion that also has a duration and an amplifier (strength) parameter.
You can get them from an IPotion object.

Importing the package

Link to importing-the-package

It might be required for you to import the package if you encounter any issues (like casting an Array), so better be safe than sorry and add the import.
import crafttweaker.potions.IPotionEffect;

ZenGetterType
ZenGetter
duration
Type
int
ZenGetter
potion
Type
IPotion
ZenGetter
doesShowParticles
Type
bool
ZenGetter
amplifier
Type
int
ZenGetter
curativeItems
Type
List<IItemStack>
ZenGetter
effectName
Type
string
ZenGetter
isAmbient
Type
bool
ZenGetter
isPotionDurationMax (also a ZenSetter)
Type
bool

Is an item a curative item

Link to is-an-item-a-curative-item

Uses an IItemStack.
Returns a bool

ZenScript
Copy
isCurativeItem(IItemStack item);

Perform Effect on an Entity

Link to perform-effect-on-an-entity

Uses an IEntity or any of its subclasses (e.g. IPlayer).
Returns void (nothing).

ZenScript
Copy
performEffect(IEntity Entity);