I mean, is not really a doubles format as much as is 3v3 with complex fusion mechanics, it barely has anything to do with how Commander works so all the comparisons end up being misleading and could be confusing. It just ends being a weird variation of FF and Inh.
1. "It's not really a doubles format as much as is 3v3"
Firstly, this OM is closer to a 6v6 rather than a 3v3. After your Dontatsu dies, your Tatsu returns to the field so you've only lost 1 mon instead of 2. I'll assume you're also saying that the OM is more like Singles 3v3, but correct me if I'm wrong. This is also not true. When your Dontatsu dies, you won't have access to another Dontatsu immediately unless you hard switch your Tatsu out the next turn. There is a lot of upside to NOT fusing. Everyone knows that there is an opportunity cost in switching because you're sacrificing using a move to better your position. Not only that, remember that a Dontatsu is not necessarily better than just 2 mons on the field. There are many drawbacks to Dondozo-Tatsugiri in standard Doubles and VGC such as the inability to switch and reduced action per turn, especially because of Protect. In conclusion, 1v1 situations will be a lot less common than you think due to the drawbacks of fusion.
2. This OM has "complex fusion mechanics"
I'm not certain if you are referring to the complexity of the benefits or the method of the fusion mechanic being too complex, but I will address both. I would like the the fusion mechanic to feel powerful, because it is the main feature of this OM. I have already mentioned the drawbacks in the previous section so the benefits must be sufficiently powerful to compensate. At the moment the only benefit I am certain of is the increased base stats. The others can be adjusted and I am open to all feedback on this aspect. I don't think the addition of base stats, type, ability and moves is too complex. We have seen other OMs just like FF and Inh which you mention later with the exact same mechanics. I don't think the benefits of fusion is much more complex than those OMs.
Let's address the other aspect of the fusion mechanic: how it occurs. Although it may seem complex, it really isn't. I think anyone who has seen the Dondozo-Tatsugiri in a WiFi or VGC battle before should be able to understand quickly. I'll still discuss why I think it is NOT complex, though. Firstly, the fusion is automatic. You don't have to do anything in your teambuilder to create a Dontatsu mon. Simply place them in position during the battle and the simulator should automatically fuse them for you. Secondly, although you might think it as unnecessary complexity, the rule that makes all pokemon only able to fuse once makes this OM much more interesting. You may use this rule as argument to support your next claim that this OM has "barely anything to do with Commander" but I will still stand by this rule. I don't think a mon only being able to fuse once is too complex to understand either.
3. This OM "barely has anything to do with how Commander works so all the comparisons end up being misleading and could be confusing."
Let's first talk about how Commander works in-game. I'll quote directly from Bulbapedia:
"When a Tatsugiri with Commander is on the same side of the field as a Dondozo, it will enter the Dondozo's mouth and the Dondozo will have its Attack, Defense, Special Attack, Special Defense, and Speed raised by two stages each. While Tatsugiri is inside Dondozo's mouth, the latter will be unable to switch out (even if Tatsugiri faints) and cannot be forced out. The Trainer will not be able to select moves for Tatsugiri, and any opponent's moves (even if it has No Guard) will miss if Tatsugiri is targeted. If Dondozo is switched in when Tatsugiri is already on the field, Commander will immediately activate and cancel Tatsugiri's selected move; any moves targeting Tatsugiri that turn will also miss. When Dondozo faints, Tatsugiri returns to its normal position in battle."
To summarize, in-game Commander has the following mechanics:
- Grants stat boosts
- Grants "unable to switch" status
- Removes Tatsugiri's action
- Immediately triggered whenever both Don and Tatsu are present
- Returns Tatsugiri to battle after Dondozo faints
I hope that you can see why this OM's mechanic is based on Commander. If you want to argue more regarding your statement, please elaborate with your reasoning and I'll be happy to discuss.
Nevertheless, I will highlight some aspects of Commander which is not replicated in this OM and address the reasons why I have omitted them. Once again from Bulbapedia:
"Tatsugiri will continue to take damage from sandstorms, as well as status conditions (such as poison) if it has already gained one prior to entering Dondozo's mouth, and the effect of Perish Song will continue normally. Commander will not reactivate if Tatsugiri faints and is replaced with another Tatsugiri with Commander; however, Commander can reactivate if Dondozo is revived after fainting."
The reason why I think an "Invincible Commander Mod" should exist is because frankly, this particular aspect of Commander makes no sense to me. Why should Dondozo retain its stat boosts and boosted Order Up when the Tatsugiri inside dies? Also, why can you switch in a new mon when you already have the boosted Dondozo? I think these are poorly thought-out aspects of the mechanic which I am not obligated to replicate. I've already stated why I have decided to ignore the fact that one Tatsugiri can Commander multiple Dondozos. I think it would be far more interesting if one Tatsu can only fuse with one Don, and a mon only fusing once per game is not too difficult to understand.
4. "It just ends being a weird variation of FF and Inh."
Let's discuss your final point. You are correct in saying that elements of this OM is the same as FF and Inheritance. Two pokemons fuse and gain access to new abilities and moves. However I would like to argue that this OM is different enough from those two OMs.
My first point is that in those two OMs, you don't need to run the fusion/donor. E.g I don't need to run Lucario to give a mon Extreme Speed, CC, Swords Dance, Justified, etc. in FF or Inh. However, in this OM, you have to run Lucario if you want to fuse it.
Secondly, the fusion mon in this OM is dynamic, not static. In FF and Inh, you choose your set in the teambuilder, and it is immutable. Meanwhile in this OM, you can fuse any two mons during the battle. One game you might fuse mon A and B but next game maybe A and C instead.
Thirdly, this is a Doubles OM. Doubles is inherently different from Singles. If you make FF or Inh a Doubles OM, it would develop vastly differently from its Singles counterpart. For example, Stall is basically unplayable in Doubles due to the fast-paced nature of the metagame. This factor should also provide a different experience to the players.
Finally, let's talk about PiC even though you didnt mention it since I think that OM is the closest comparison you can make. Nevertheless I will argue that this OM is unique enough from PiC. The reason is the difference between fusion and shared attributes. In PiC, both mons share moves and abilities. By switching your mons around, you can give different moves and abilities you your mons. Meanwhile in Commander, you are locked in when you fuse. You can't switch out and you only have one move per turn. You combine into a "super" mon with new type and higher stats. Support moves such as Helping Hand, Follow Me and Heal Pulse suddenly become useless after fusion. I daresay this OM is much more punishing in that regard.
I hope this answers your concerns. If you have more feedback then I would be glad to hear it. If you don't understand some points then I'll be happy to elaborate further.