Gameplay in the coliseums of The Underdome consists of waves and rounds. Each round consists of five waves.
- Starter wave: This is a relatively easy mixture of enemies that will be fought in the next couple of rounds.
- Gun wave: Every enemy will have weapons. No skags or psychos will be present, only regular bandits/brutes or Crimson Lance.
- Horde wave: Psychos - Many psychos. All types (regular, burning, badass, and midget).
- Badass wave: Don't be intimidated. Few of the enemies are actually badass variants, but each will come with a couple of smaller equivalents; bandits are upgraded to brutes, Lance Infantry are upgraded to Engineers etc.
- Boss wave: A random boss is selected to be fought, as well as a few henchmen. These include Nine-Toes and his skags, Bone Head, Baron Flynt, Hanz and Franz (always without henchmen), Master McCloud, King Wee Wee, Reaver, Sledge, One-Eyed Jack, Taylor Kobb.
- At the end of waves one through four, Moxxi will drop two types of Supply Packages. One of Ammo consisting of 18 Revolver, 18 sniper, 24 Shotgun, 54 Repeater, 54 Combat Rifle, 72 SMG rounds, and 2 Grenades, the other being Mega Healing Vials. The beginning of the supply drop is signaled by a little brown box attached to a parachute and Fireworks. These drops will land all over the arena and only last a few seconds before disappearing.
- Some enemies will drop Super instaheath vials that stay until the Round is finished.
- A random selection of weapons will appear at the bottom of Moxxi's tower once the boss and his henchmen are defeated. Players will have about ten seconds before the weapons disappear again.
- It appears that not all players see the same selection of items. Some weapons will only be visible to some players, so be sure to check the drop individually.
- It is possible to get loot from enemies as well, but it's extremely rare.
- Mordecai's Swipe skill will generate additional item drops, though they are usually money or health, with the extremely rare weapon drop.
- In multiplayer, on PC, the host will get the 'Wave Over' screen and can do nothing but hit 'Enter' and continue. So if one of the characters has a regenerating mod for the team, be it health, shields, or ammo, be sure to use these few moments of peace to restock the team! Issues have been fixed, apparently it is not a glitch but an exploitative break intentionally included.
- On any round with Close Combat active, The Bessie sniper rifle's accuracy is unaffected when zoomed. Confirmation needed.
Every round will increase in difficulty. Every five rounds the amount of enemies to kill increases. More enemies will teleport into the arena over time within each wave. If all the members of a party are defeated, then the whole party starts at Wave 1 of the previous Round.
|1||-4%||-6%||-8%||none||Starting out easy|
|3||0%||0%||0%||1||Welcome to average|
|5||+4%||+6%||+8%||2||Professional grade tournament||Last round of the Small Tournament|
|6||+6%||+9%||+12%||2||Are you man enough?|
|7||+8%||+12%||+16%||2||I eat round 7 for breakfast, do you?|
|8||+10%||+15%||+20%||2||Kill kill kill|
|9||+12%||+18%||+24%||2||Brick's Mama got past this round|
|10||+14%||+21%||+28%||3||You rock, I'll roll|
|11||+16%||+24%||+32%||3||These guys take a lot of hits|
|12||+18%||+27%||+36%||3||Lock & Load|
|13||+20%||+30%||+40%||3||I'm not dead yet|
|14||+22%||+33%||+44%||3||Bigger, stronger, faster|
|15||+24%||+36%||+48%||4||What, did they just add another rule?|
|16||+26%||+39%||+52%||4||Suck it down|
|17||+28%||+42%||+56%||4||Better hope your guns deal a lot of damage|
|18||+30%||+45%||+60%||4||Game over man, game over|
|19||+32%||+48%||+64%||4||They deal how much damage?|
|20||+34%||+51%||+68%||4||Grade A - Badass||Last round of the Big Tournament|
Rules, also referred to as Moxxi's Maxims (similar to "Skulls" in Halo 3: ODST Firefight, basically Power-ups or Modifiers) will be introduced at:
- One modifier after the 1st round
- Two at the start of the 5th round
- Three at the start of the 10th round
- All four at the start of the 15th round
Examples are listed below.
|*weapon* Challenge||A random weapon type is chosen (for example, Shotguns). That type does more damage and everything else does less. Eridian weapons don't seem to be included.|
|Body Shots||Critical hits do less damage.|
|Close Combat||Players will be less accurate, but will do much more damage.|
|Elemental Challenge||Elemental attacks will work better, normal attacks will do worse.|
|Headshot||Critical hits do more damage, everything else does less.|
|Beef Cake||Enemies take less damage from attacks.|
|Dead Aim||Enemies are more accurate.|
|Dodgeball||Enemies actively dodge attacks.|
|Ironhide||Enemies have better shields.|
|Kick Ass||Enemies will deal more damage.|
|Loaded||Enemies have larger magazines.|
|Overclocked||Enemy shields regenerate faster.|
|Regeneration||Enemies regenerate health.|
|Spastic||Enemies move and reload faster.|
|Weapon Masters||Enemies spawn with higher quality weapons.|
|Get Some Air||Low gravity. (Formerly impossible jumps may be tried to reach new sniper spots.)|
|High Speed||Players and enemies move faster.|
|Naked||Your character has no shields, but will slowly regenerate health.|
|Vampire||Your character's health constantly degenerates, but can be refilled by killing an enemy. If your character gains a second wind, both health and shields will be fully replenished.|
If a player dies and fails to get a second wind in a multiplayer game, they respawn in the Penalty Box on top of Moxxi's tower. The character will be stuck up there, but can still help the rest of the team by shooting down on enemies. Do not forget to throw grenades! Transfusion are a great asset to your friends still fighting on the ground. Players in the Penalty Box will not be targeted by enemies and their health will not drop below one point. Players will respawn at the bottom of the tower once the wave is finished, or the entire party is wiped out. If the entire party is wiped out, the whole party starts at Wave 1 of the previous Round.
If a player dies and fails to get a second wind in a single player game, they respawn in the Penalty Box for a short while as a formality. Then they will respawn back at the foot of the tower, and restart the tournament from the first wave of the previous round.
Unlike respawns in regular gameplay, no money is lost on death.
Players will be rewarded after the completion of each round. After defeating the boss, a few weapons a few levels below the host's own will spawn under the player spawn point. These weapons are usually of good quality, and players may have a fair chance of finding an Eridian weapon. Be sure to grab them before the timer runs out, because they disappear.
Having more than one player in the arena fighting increases the quality and amount of weapons after each round.
- Main article: Underdome glitches