Axle the Beast

Okay, I think I'm getting a picture of this then. It's a good idea to have some diversity in the bosses, so each boss battle is different, while they all still match up with the kind of gameplay (it's typically not a good idea for a boss to feel like it's from a different game unless the whole game is like that between individual sections.) It seems like your game is a fairly straightforward action platformer concept with a vaguely anime or action movie style, and with the dashing, an emphasis on quick maneuverability.

I think a good boss to have would be something small that moves quickly. Perhaps something vaguely reminiscent of a ninja, but it could also be a shadow or even a robot or creature. Something that's hard to catch but might not do a lot of damage outright. It could either attack you physically or even shoot at you (especially if it's a robot.)

Aside from that, perhaps something medium sized that keeps its distance from you, attacking from the air or from some other vantage point, requiring some patience to set things up. Something airborne, like a bird, something aquatic, or even something that climbs and jumps, or just something very large where the weak point is hard to reach.

Even with lowest cost, my battery died in sleep mode

Why was it in sleep mode though? Did you have a game running or...? If the internet is on while it's in sleep mode, it can be downloading stuff. Even if it's not doing anything, it clearly consumes power. Sleep mode isn't generally something it should be left in indefinitely. If you're not going to use it, you should turn it off.

We talking strictly the Classic series or the entirety of the Mega Man franchise? If it's the former, Mega Man 8. If it's the latter, the Zero series, and most specifically, Mega Man Zero 3.

Zero is the perfect conclusion to the long-running storyline of the franchise. In terms of gameplay, story, and emotion, it's a big feast for any longterm Mega Man fan.

You know that right circle pad? I see no reason why anyone would buy it unless it expanded the battery life for the 3DS by at least 5 hours.

I don't get what the stigma about the Circle Pad Pro is. It's an optional add-on, that every existing game that supports it does not actually require. I've played the Snake Eater 3D and Resident Evil: Revelations demos. They work fine without the Circle Pad Pro, but I can guarantee you they'd be better with it. All it does is add more buttons and some more quicker functionality, particularly with shooters, for the crowd that this appeals to. It would have been better to simply include it as part of the console itself rather than a peripheral, but it does no harm to anyone.

Battery life is a little low, yeah. Wish Nintendo had done better on that. But it's not so bad that it's completely crushing; have you turned the brightness all the way down and shut down the wireless while you play offline? That should reduce battery consumption.

I am not looking for the pattern of the boss's attack. Just what they should look like.

If you're looking for ideas on what to make them look like, it would help to know what kind of setting your game has. I can't come up with ideas that befit your game without a little more information.