Technically when the jedi use it it is considered more of a defensive tool. ;)

Also as for unreal: What, no 8-ball gun? :D

After not determining what kind of game - the dice can be a powerful weapon. :-)
Because if you throw in yatze, backgammon or risk exactly the eyes you just need - it does not get much better than that.
If the opponent dices exactly, it is of course always "cheating"...honestly i had the biggest quarrel with family and friends about "wrong/right" dicing ... so I would say these are "mega" weapons.

Pan, PUBG. The sound and the satisfaction of having an opponent out of the way with an ordinary household appliance is unequaled. Now that it has been introduced that you can throw the enemy to dead with the pan ... ... Fun factor 100%.

Aerondight, Witcher 3. The quest and presentation for receiving the silver sword is simply awesome. The sword itself is also "nice" (...).

The 8-ball is great sure, but it can't quite match the visceral carnage of the flak cannon, i.e. jagged metal shotgun

Gravity Gun from Half life 2.
BFG 9000 from DOOM.

Agreed, I just love the sound/motions it makes, and the whole way you first get it. :)

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All versions of the BFG or a certain one?

I myself love em all. :D

2016 one :)

Cool cool.....that game has some nice weapons(and mods).

Agreed.

Though I still have to hold D3 at the same place in my heart(as I played it[both versions] so much that I practically know it by heart). :)

Fallout 1: Plasma Rifle. I've always found it so engaging, proper '50 pulp fiction.
Fallout 2: Gauss Rifle. I love everything about this gun, especially the sound it makes when you fire it. From the moment I read its name, I knew it'll be my favorite weapon.

Edit: If I have to choose a shotgun variant: Pancor Jackhammer(which is also in Fallout 2)

- Acid Perfume (No One Lives Forever). Completely overpowered when enemies are charging you in tight enclosed spaces (as long as you don't step into the mist yourself...)

- Chemical Thrower (Bioshock). A gun that shoots fire, ice & lightning all in one? Great vs the Big Daddies.

- Firemace (Heretic). There's just something oddly satisfying about flinging huge metal balls down the same staircase that a group of enemies are heading up...

My preference is for weapons that have effects other than damage, particularly healing. For example:

Final Fantasy 2, 6: Healing Staff, which heals using the physical damage formula.
Final Fantasy 5: Healing Staff, which has no effect, but additionally has a 100% chance of casting Cura (which, it's worth noting, is subject to Reflect, but is still considered physical for counter purposes (IIRC), so an enemy that counters physical attacks will counter twice.)
Lennus 2: Life Corsage, which restores 300 HP to the entire party and revives fallen party members (for free, but note that 300 HP is not a lot in this game).

I believe Baldur's Gate has a cursed weapon called the Vampiric Blade which reverse drains when it hits; if it gave the wielder health regen it would be a really nice weapon, but it doesn't. (It's a shame that the sequel seems to be rather lacking in terms of cursed items that are worth using.)

Icewind Dale 2 has a weapon that heals when it hits; on Heart of Fury mode, it's replaced with a weapon that heals more.

For a non-healing effect, how about the Saw from the first two SaGas, which kills its target depending on how the attacker's STR compares to the defender's DEF? (In SaGa 1, it works if STR < DEF; in SaGa 2, it works if STR + 10 > DEF IIRC, though SaGa 2's version halves the left side of the inequality if the target has OWepaon.)

As far as weapon attacks are concerned, damage as an effect is really overused; I want weapons with more interesting effects! (Many games also overuse this effect with special attacks and sometimes even magic.)

This reminds me of a similar mechanic I love in weapons, at least in RPGs: vampiric effect. Given the chance, I always go for vampiric effects and weapons in most games. Especially in Neverwinter Nights.

Too bad vampiric effect is utterly useless in most action RPGs I have played. Cardinal sin as far as I'm concerned.

Some more things, because... why not.

Series 3 Plasma gun from Doom 3 - Tell me about a reality where it isn't satisfying to listen to this thing fire or reload. I'll tell you that such a reality is one where joy doesn't exist.

Razor Wind from Turok 2: Seeds of Evil - You remember the film Krull and how ridiculously awesome Colwyn's weapon the Glaive was, right? The Razor Wind is like that, minus the ability to use it like a psychic surgeon.

Blade of Darkness: Ianna's Sword