I'm probably late to the party, but I'd like to contribute to this. I haven't in a long time, but I used to fight in the arena section, and my god does the unwillingness of people to lose make it hard to enjoy. So I appreciate an attempt to introduce roll-based mechanics into this sort of cinematic fighting format.

But I think that out of all possible options, D&D 3.5 is a terrible system to execute this in. The main reason is that while it offers lots of character customization options, your options in combat (as a martial, at least) are extremely limited. The system often requires significant investment just to let you do fairly basic things. In a free-form battle, things like tripping, grappling and disarming are just some of the tools at everyone’s disposal for combatting their enemy. You don’t need to state on your CS that your char is good at tripping to be able to use it in-game. But in 3.5, each of those requires a feat to be able to do it without provoking an opportunity attack.

As a result of this design philosophy, low-level martials are one-trick ponies. This gets better at later levels, but there’s still little improvisation to be had: All the tools at your disposal are pre-determined. The issue of the battle being won in character creation has already been brought up, and is inherent to many systems, but D&D 3.5 suffers from this problem more than any system I’m familiar with.

Other problems that make 3.5 a poor choice for this kind of game:
- The class balance is quite poor and there is enormous potential for power gaming.
- It’s a slow and tactical game with a strong focus on grid-based movement. Opportunity attacks are not so much a single mechanic as they are an entire subsystem within the game. This design clashes with the cinematic nature of arena battles.

Point is, it would take tons of adaptation to make D&D 3.5 usable in a cinematic arena format. I suggest using a lighter system. D&D 5e is an option, since it’s easier to digest, more balanced, and less restrictive. But one of my favourite RPGs is the incredibly light-weight Barbarians of Lemuria, which has simple and unrestrictive character creation, an emphasis on creativity in combat, and a free-form magic system that lets you replicate almost any character concept. It strikes me as perfect for this purpose. The downside is that because it’s so rules light, you often need to make rulings on the fly. There is, for instance, no definitive ruling on the effect of being prone. So it requires a lot of goodwill and cooperation between players. It also needs a few houserules for balance, but it’s very easily modded due to its simplicity. You can easily find the Barbarians of Lemuria basic edition online if you want to take a look. There are other editions, but I use the basic.

Let me know what you think of my thoughts. I’m interested in making this idea work.