You may still use a weapon you aren't Proficient in the use of, but you may not add your Proficiency Bonus to your Attack Rolls.
If you do not meet a Prerequisite for use of a weapon you may still use it, but all attacks using it will have Disadvantage.
Weapons and Stands:
Normal weapons cannot damage Stands. However, if you take the Energy Imbuement
Feat, when a weapon is imbued (or incorporated into the Stand itself) it deals Stand damage instead and may now damage Stands
If your Stand wields a weapon or has a weapon incorporated into it, it may attack using its own stats rather than that of the User.
For example, Strength becomes Power, Dexterity becomes Precision, and Constitution becomes Durability.
Weapon Attributes
AC Bonus: This weapon grants a bonus to your AC while it is equipped.
Ambush: This weapon always crits when attacking a Surprised target.
Bulky: This weapon must be braced using a Bonus Action in order to attack with it. Once braced, you remain braced until you move.
Complex: This weapon takes a total of three Attacks to reload.
Concealed: This weapon grants a bonus to any Check made to conceal it.
Conductive: Energy currents, such as electricity or Ripple, may be run through this weapon."
Firearm: This weapon makes a loud sound which can be heard up to 0.5km away. It also jams if a natural 1 is rolled while using it. This weapon's ammunition doesn't function when wet.
Flame: When a targeted creature or object takes fire damage from this weapon, it is set ablaze (assuming the target is flammable).
Hunker: While holding this item, if you've not moved this turn, you may gain Cover as a Bonus Action until the start of your turn, though this also reduces your Movement Speed to 0.
Light: This weapon is light and easy to handle, allowing you to make an additional attack using another Light weapon in your other hand as a Bonus Action.
Point Blank: This weapon does not impose Disadvantage if fired within melee.
Radius: This weapon forces all creatures within a certain radius of the target to make a Dexterity Saving Throw, taking half damage on success and full damage on failure.
Ranged: This weapon can fire up to its Short Range, or as far as its Long Range with Disadvantage. Firing within melee imposes Disadvantage.
Reach: This weapon can attack targets from an additional meter away.
Reliable: This weapon does not jam if you roll a natural 1.
Reload: This weapon can be used a limited amount of times before needing to be reloaded. Reloading takes a full Attack.
Remote: This weapon can be detonated as a Bonus Action from up to 1km away.
Return: After making a Thrown Weapon attack with the weapon, you may use your Reaction to catch it, putting it back in your inventory.
Siege: This weapon deals double damage to objects.
Timer: A timer may be set on this weapon, detonating it once the timer runs out. The timer may be set for up to 12 hours.
Thrown: This weapon can be thrown up to its Short Range, or as far as its Long Range with Disadvantage. Once thrown, this weapon must be picked up in order to be used again (unless it is an explosive, in which case it is destroyed).
Two-Handed: This weapon requires two hands to wield, and is difficult to holster or conceal. May be carried (but not used) with one hand if desired.