The Legend of Korra

I played this on Normal.

For this solution, I will be focusing on the mechtanks (yes, more than one) you will be fighting in Chapter 4. The other big enemies would be the Triple Triad trios which you had already known how to beat if you passed Chapter 3.

For a mechtank, the trick is to avoid its ranged attacks and counter its melee attacks.

Use R2 to dodge and remember to only press up to 3 in succession at a time. On the 4th successive press, Korra would stop to catch her breath and be vulnerable (I really don't know why Platinum put that pause in, honestly).

Use L2 to block and counterattack, which will be very important in unlocking Korra's earthbending and acting as your strongest attack.

The first mechtank will have a few different attacks:

1) a bolo shot that will bind Korra so that it could...
2) ram rush and knock Korra down severely, opening her to...
3) an electric shock from below as it sticks a cord underground to send shock blasts up, usually 2 in succession
4) also an electric lasso that would pull Korra in and slam her down if you don't press O at the button prompt
5) various melee attacks (swipes, wide arcs, or ground pounds)

The best way to start the fight is to dodge its initial volley and its ram rush.
Then turn around and hurl water balls at it until it comes up at normal speed to punch you.
Block and time that block well so you can counterattack by pushing both control sticks up at the prompt.

After close to a minute of fighting, Jinora will appear and say she knows how to unlock Korra's earthbending.

At this point, don't take potshots at the mechtank, because its lifebar will be replaced with a 0/4 counter and no attack would take down its life.

Focus on waiting for the mechtank's melee attacks to block and counter them 4 times.
After this, you will finally unlock earthbending and restore your health bar to max.

At this point, you will be switched to earthbending powers, but I actually recommend you press L1 to switch back to waterbending so that you can keep hitting the mechtank from afar. And when you counterattack, you can actually sometimes encase the mechtank in ice and freeze it. hehe

Switch bank to earthbending (R1 is quickest way to switch from water) when you've successfully counterattacked and stunned the mechtank to pause for a few seconds. Use your strong earthbending attacks to whittle some health down before backing away as it wakes up.

At the last half of its second lifebar, the mechtank will turn red and be more frenzied. It will be faster. And it will send up a series of 3 electrical shocks instead of 1 or 2.

This will be a long fight.
You will have no health powerups available during this battle.
And the mechtank will have at least twice the life of Korra with better armor.
I'll tell you how to make it easier later.
But first, just remember again that dodge and counterattacking are your best friends in mechtank fights and you should fare pretty well.

The second mechtank will appear after the Naga rush segment (be sure to make use of new bending abilities like water shield and the earth pillar double jump).

Once you face off against the second mechtank, you will notice it has a different right arm than the first.

This right arm is actually an electric magnet.
1) It can charge its punch to be a shock punch that you should avoid.
And 2) it can also suck in a car from offscreen to launch at you. So when you see the car appear in its hand, dodge!

But at least you have a wider arena this time with many vehicles around that if broken often give you health.

So use the same tactics as before, combine the two new moves and responses to them in, and you should get through fine.

Still, after reading this, if you think "man, this is going to be hard", you may be right. The mechtanks do hit pretty hard and you'd be really lucky if you can avoid every single hit.

That's why I also recommend you check out the Shop (most easily accessed via game over menu ;>) and buy the Healing talisman. This will allow Korra to regenerate health which - as long as you don't get TKO'd - would be a lifesaver. For TKO failsafes, you can also buy Katara's Oasis Water to revive you on death.

The rest is up to you and how many spirit points you are willing to let go. ;)
Also remember that you can equip up to 4 talismans and/or items in Korra's room.

More importantly for trophy hunters, maybe, are the two trophies you get for 1) buying from the store and 2) equipping a talisman/item on to Korra. ;)

Whatever your reason, the option is available. :)

Good luck out there, Avatar!