First off, this isn't a variant but I didn't know where else on my site it belonged so I'm putting it here. :)
There are a great many variants and such, but I have yet to see a listing of some mini-games you can play while in Diablo. The fun I've had playing some non-variant/non-quest games has been great, so I thought it'd be a good idea to collect some of the ideas and put them on a web page.
1) Tag
Much like its real life counterpart, Diablo "Tag" plays by the same type of rules. Get a few friends together and have fun!
Where to play?
-The Church levels are nice for clean cut level designs.
-Catacombs is much like the church levels except for it's sometimes lenghty designs.
-Caves is a great place. You can hide amongst groups of rocks and it can be genuinely hard to find people.
-Hell is at times too symmetric, but it would still work.
How do I play?
Here I will list some things to think of before playing.
"It": Someone always has to be "It". Be sure make it clear who this person is. Can you kill the person who is "It"?
Tagging: You must tag opponents in order to become un-"It". What is defined as a "tag"? Is it a kill? Is it one connecting spell? Is it a melee attack? Is it an arrow? What happens if the attack is blocked? Be sure to make it clear what constitutes as a "tag."
To Clear or Not to Clear?: You may opt to clear a level and make for less dangerous gameplay. Not clearing the level, however, can add much excitement because then a person may hide with -80% lr amongst some monsters for protection. The monsters would leave them alone, but if you got close they'd go after you.
Spells: Spells add much to gameplay. Using spells can make the game go much faster, too. Not using spells may make for long drawn out gameplay, but also for a unique style.
2) Duel Variation: Griswold's Blue Light Special!
This is a duel that I thought up. I made it because I was a bit tired of run-of-the-mill duels where everyone wants the nicest outfit and the most damaging attack. Well, here's how it works...
-You may not use any spells during the duel itself, except for the Official Guardian Timer to initiate the fight. A Guardian Timer is when someone casts Guardian and when it goes out the fight begins.
-You may not use any items that you came into the game with. The items you will duel with will all be bought from Griswold's Basic Item Section when you first enter the game. (No shopping for a better selection. :)
-Clear an area on a level to duel. (You may use spells and items you entered the game with to do the clearing, of course.)
-I find that this duel is best attempted with characters of the same level. This is because of what types of basic items Griswold will sell and the statistics of the players will be corresponding to some extent.
Beware of mages that abuse the Mana Shield bug so that they do not suffer from hit recovery. But, then again, there are no spells allowed so they can't use Mana Shield.
3) PONG!
Diablo Ping-Pong! That's right! All the fun of the original game, only deadly!
-Clear out lv 16 except for Diablo.
-Position 2 players in a wide area and mark off the perimeter with lines of 1 gold pieces so you will know where the boundiaries are located.
-Lure Diablo into the middle of the arena and the have the 2 players stand on the outside of the gold ring/square you've made.
-Use Telekinesis to knock Diablo to your opponent! Keep using it and try to keep D over there! If you can knock him past their line of gold then you get a point! (Diablo must be ACROSS the line for it to be counted as a point. Simply standing on the line does not count.)
This is best played with Sorcerers because they can cast the fastest and have the most mana. Warrior would be harder to do this with because of slow casting time, but then again, a Sorcerer beaten by a Warrior in this type of game could be pretty embarassing for the Sorcerer.
I've played a pseudo-version of this and it was immense fun to see D go flopping back and forth.
4) Graphite Man
Basically, this is a variation on Iron Man. It's a lot easier, but still may be fun.
-Start game off with a number of players who are lv 20+
-Do not use any items/pots/scrolls/gold that you brought into the game
-Go to the Church (Norm, nite, or hell depending on what the players decide) naked while finding items and such along the way
-Fight your way to 16 and kill D without any trips to town for identifications or potions
-Goal: To kill Diablo using only the items that you found from 1-16