Can PCs make cursed items in D&D?
The magic item creation rules do not discuss PC creation of cursed items. They appear to have assumed that only the GM would create them, and those are created by fiat.
If a player, however, wanted to attempt to strike at a villain by creating an item that looked like a beneficial item, but was instead cursed, are there any mechanics to support this?
The item is intended to be 'delivered' to the villain by 'accidentally' leaving it insufficiently protected.
The item creation rules certainly allow creation of cursed items. The DMG gives guidelines based on cost on pages 129 and 130.
The creation of a magic item is a lengthy, expensive task. To start, a character must have a formula that describes the construction of the item. The character must also be a spellcaster with spell slots and must be able to cast any spells that the item can produce. Moreover, the character must meet a level minimum determined by the item's rarity, as shown in the Crafting Magic Items table.
An item has a creation cost specified in the Crafting Magic Items table (half that cost for a consumable, such as a potion or scroll). A character engaged in the crafting of a magic item makes progress in 25 gp increments, spending that amount for each day of work until the total cost is paid. The character is assumed to work for 8 hours each of those days. Thus, creating an uncommon magic item takes 20 days and 500 gp.
\begin{array}{l | l | l} \text{Item Rarity} & \text{Creation Cost (gp)} & \text{Minimum Level} \\ \hline \text{Common} & 100 & 3rd \\ \text{Uncommon} & 500 & 3rd \\ \text{Rare} & 5,000 & 6th \\ \text{Very Rare} & 50,000 & 11th \\ \text{Legendary} & 500,000 & 17th \\ \end{array}
For example, creation of a very rare cursed item would cost 50k GP, require a special recipe, at 25gp per day per 11th level character. This would take 333 days for a six person party.
Generally, magical items of that power are meant to be found, not created.
