Interesting and challenging arena battle?

Soliciting suggestions for opponents (enemy combatants, beast(s), etc.) for an interesting and challenging arena combat for a Dark Sun game set in Tyr. The PCs are 3 and 1st level: Human Sentinel|Warlord (living zephyr companion), Halfling melee Rogue, Mul alhulak Fighter.

Said encounter should be a tactical and resource (APs, Dailies) challenge for the PCs without pushing the envelope beyond the pale AND should be a likely scenario for what would actually be fought in an arena in a major city. (For example, it seems to me that an Id Fiend (L1 Solo), with its particular powers and traits, may be pushing the challenge level just a little too high AND ALSO not be the kind of thing officials would introduce into the city in case it escapes, etc.)

Thoughts?

For one: Arena terrain should be interesting. My go-to is making the center have some sort of "high ground" platform that gives CA if you do a melee attack from high to low ground. Next, add cover. You need a good way for a melee combatant to circle around the edge of the arena while avoiding ranged attacks. Finally, I'd throw in random hazards of "Suddenly, standing here is difficult terrain + damage at start of turn"

Slowly filling the arena with piranha infested water is great for adding tension!

A few gelatinous cubes around the arena can make movement interesting.

I've found the stuff from Gladius works well. A series of non lethal games mixes things up well.

King of the Hill - each team gets a point for each round they control the top of a pile of boxes.

Domination - like king of the hill but there are multiple hills.

Crowd Battle - who can get the crowd more worked up within a certain amount of time?

Totem - defend your totem while going to destroy your opponents.

Make them use those positioning powers!

Thanks for the responses, folks. I have some definite ideas for terrain and alternate goals. Specifically, I'm looking to brainstorm a challenging and likely opponent(s) set for the PCs, i.e. their foe(s). (I reckon a thousand minds are better than my one feeble facsimile thereof....)

Here, take a look at this: https://1drv.ms/f/s!As7yoWrpdEtvqQq7vcv-ZyM2dEF1

Specifically look in the "Old" and "Cards" folders. I was beginning to redo this project and stuffed all my old work there. A good deal of the setting info is Mystara specific but it is easily stealable since Thyatis is basically Rome. The gladiator cards are designed to work with the MM3 on a Business Card rules - just add the appropriate numbers for higher level gladiators.

Have fun!

edit: Might as well include two non-combat games:

Siri Mpira
Two teams of four – three “hiders” and one “seeker”. There are sixteen barrels on the field in a 4x4 square each 20’ away from each other. Each team starts 20’ from each side of the barrels with a colored ball. They try to hide which of the three “hiders” has the ball before crossing a line within 10’ of the barrels. All team members must stay in a group until they reach that line. Once they cross the line the team has ten seconds to hide the ball in a barrel. Once hidden the hiders must leave the field and the seekers must find the opponent’s ball and carry it across a finish line that is 50’ on the opposite side of the barrels. First one across gets a point. Each team member takes a turn as a seeker and then the team with the most points wins. Ties are determined by extra rounds.
Each attempt to hide the ball requires a Thievery vs. Perception check with each participant involved in hiding the ball adding a +2 to the Thievery check. Searching a barrel is a standard action – taking it is part of that action.

Handball
Two teams of 4. A 100’ x 40’ field with suspended 5’ rings hanging 10’ in the air at either end. Chosen team starts with something like a soccer ball that they have to carry to the other side of the field and toss through the opponent’s ring. The ball must be carried and cannot be kicked. If the ball hits the ground it is given to the team opposing the one last in control if it. Whomever scores 5 first wins.
Passing
• The ball has a range of 2/4 and confers no weapon bonuses.
• Throwing the ball accurately requires a ranged attack against AC 10.
• Catching the ball requires a Dexterity check DC 10.
• An adjacent opponent may choose to try and block a thrown ball. He adds his Dexterity bonus to the AC if by the passer or the catch DC if by the receiver.
Blocking/Tackling
• A character may attempt to block any time they could make an opportunity attack. Make an opposed Strength check – success means the target of the block is stopped and the blocker may shift in front of them. Success by more than 5 means the target is knocked prone. Loss by more than 5 results in the blocker being knocked prone.
• Only the ball carrier may be tackled. Treat the same as a block only the runner is grabbed if he isn’t knocked prone.
• An opposed Dexterity check is used to strip the ball from a grabbed opponent.