As the title says it, I need help creating a potion that increases the player's move speed a lot, the vanilla's move speed is too slow for my mod's armors that uses the move speed potion. Can anyone help me? From what I understand I need to create a class that extends Potion but I'm not sure how to proceed from there.
Potions that modify the player's attributes (move speed, attack damage, etc.) use the attribute modifier system by calling Potion#registerPotionAttributeModifier with the arguments needed to create an AttributeModifier. This modifier is then applied to any entity affected by the potion.
Call this method with the IAttribute (SharedMonsterAttributes.movementSpeed), the string form of a random UUID (call UUID.randomUUID once and then hardcode that UUID in your code), the amount to affect the attribute by and the operation to apply the amount (see the wiki page I linked earlier for an explanation of the operations). Look at the Potion class to see how vanilla uses this method for its own potions.
Please don't PM me to ask for help or to join your mod development team. Asking your question in a public thread preserves it for people who are having the same problem in the future. I'm not interested in developing mods with people.