As has been the case for every iteration of the Megaman Battle Network/Starforce series since Battle Network 2, the hero of Megaman Starforce 2 can transform into several different special forms that are unique to this particular entry in the series. This time around, the system is called the "Tribe On" system, in which Megaman can fuse with an artifact left behind by one of the "Tribes" in order to transform into a more powerful state. At the surface level, it looks like a cheap gimmick like some previous versions of the concept, but it actually works quite well, and I like the system quite a bit. It has some flaws, but it does add some value to the game.
Before I go any further, I have to say that I think the particular "Tribes" that are used in this game are all ridiculous. I'd admit that I think ninjas, dinosaurs, and medieval berserkers are all cool things just as readily as the next guy, but throwing them all together with no rhyme or reason like they do in this game is just cheesy, and it gets worse when you start using the "Double Tribe" system to get Ninja Dinosaur Megaman. The game has enough trouble trying to replace the coherent and fun constellation-based naming scheme and alien-based plot established in Starforce 1 with some plot based around a tenuous connection between the lost civilization of Mu and UMAs like the Abominable Snowman and the Loch Ness monster, and adding a group of randomly selected "Tribes" with no clear connection to anything else does not help that uphill battle in the least. If the Tribes were rooted in UMA creatures and ancient or mythical civilizations like the Mayans or Atlantis, it might have worked, but as it stands it just doesn't. Fortunately, once the poor naming scheme is safely ignored, we are left with one of the best Megaman transformation systems to date.
The advantages of the Tribe On system start with the actual mechanism used to enter the form. Starforce 1 used a clunky system of "Starforce Cards" in which you had a single Battle Card in your folder that let you transform if you got lucky enough to draw it, which became rarer and rarer as you slowly acquire things like Brother Cards and Legend Cards that dilute your Folder. Starforce 2 replaces this by linking the Tribe On ability to Brother Cards, so you actually greatly increase your odds of transforming by forming more BrotherBands, which is far more appropriate given the themes of the Starforce series and is a lot more fun. In addition to this, Starforce 2 gives you an optional ability that lets you start every battle in Tribe On form, which adds to the visibility and usability of the form.
Starforce 2's system has a few more advantages over the Starforce 1 system in that different forms actually have enough variation and power in order to make using the different forms worthwhile. These forms combine the traditional abilities like passive elemental bonuses, the "Super Armor" and ninja substitution abilities, the ability to charge Battle Cards to get new effects, and modified Megabuster charge shots with Starforce 1's incredibly fun Star Force Big Bang attacks to get a very solid result. These forms have weaknesses, but they are unquestionably worth using, and just as importantly they are all clearly differentiate enough that each Tribe On form has its own unique value and can be used with its own strategy. While this is not unique to Starforce 2, it is certainly an improvement over Starforce 1's lackluster forms.
My biggest praise, though, goes to the development of the "Double Tribe" system, which strikes a fine balance between giving proper emphasis to the Tribe form corresponding to the player's version that is important to the story and allowing the player to experiment with the abilities of the other Tribes. With this scheme, you can add the power of a Brother's Tribe on top of the Tribe determined by which version you are using, so if you choose "Saurian" as your Tribe you can use the base Fire Saurian form, as well as the Saurian Ninja and Saurian Zerker forms that use the element and weapon of Ninja or Zerker but use the same basic powers as Saurian. As a whole, this system has the same focus on a specific form that some older Battle Network games had, such as Battle Network 6's focus on the Gregar and Falzar forms, which helps keep the story and gameplay in sync and makes version important (avoiding the pitfall of Starforce 1 where, once you form a few BrotherBands, you can use forms from different versions equally well). At the same time, it gives you a fair amount of flexibility and rewards forming BrotherBands with people of different versions. I particularly like the way Megaman's character model and abilities are different depending on whether he is in Saurian Ninja or Ninja Saurian forms. The only flaw I can think of with this set-up is in the Double Tribe Link force Big Bang attacks, because they don't make the distinction between whether you are Zerker Ninja or Ninja Zerker, which leads to problems like the fact that I can never make use of the Zerker-style triple slash Big Bang attack, or the fact that Ninja Saurian uses a shuriken volley even though he is not holding any shuriken (and is using the Dino Cannon instead).
Finally, I have to mention the Tribe King, the ultimate form you achieve by combining all three Tribes. This is probably the first form in the history of the Megaman franchise that really deserves the term "ultimate form" (I always found Megaman X's "Ultimate Armor" to be more bark than bite). The fact that it has all of the abilities of the three Tribes combined, a very powerful Megabuster charged shot, and an unstoppable Big Bang attack would be enough to cement that title, but the Tribe King's ability to double the power of every Battle Card goes well over the top and wanders into the realm of "much too powerful". I like the fact that it makes gathering all three tribes worth the effort, and I like that an "ultimate form" actually exists, but it is just a little bit too much. Getting Tribe King essentially means instant victory, which means a boss fight or multiplayer match can be decided simply by a player getting a little bit of luck. Also, I am sure the game artists put in a valiant effort, but any attempt at making a fusion of Megaman (himself a fusion between a kid and an alien), a dinosaur, a ninja, and a medieval warrior look impressive and cool was doomed from the start.