Have you fixed engine shaking/rattling Prius 2010 with misfires codes

The fire in the cylinder getting quenched by the seeping head gasket leak puts the fire out in the cylinder which causes horsepower loss and more of an imbalance between the ice and the motor generators when this happens this causes the torque plate in between the engine and the transmission to flex to the extreme limit of the travel of the springs and then it slams or makes that noise something to this effect. If this goes on too long it will cause a rod to get bit and then when you put the cylinders on top dead center and or bottom dead center they don't all look the same sticking up out of the block then you need to replace the reciprocating mass or the center section of this modularly constructed motor with an open deck design which is inherently somewhat weaker than regular castings of blocks and heads and so forth but it's much lighter weight and things like that. But once you destroy one it's a throw away.

 

You have a bad head gasket.

How many miles on the car?

 

Second this. Also, how long have you had it?

Trying to glean what you mean: you had a Toyota dealership looked at it, they think it's a failing head gasket?

Just my opinion: dependant on your miles, the EGR system, including the EGR passages, will be clogged with carbon. The system was new for 3rd gen Prius (and Prius v), and in hindsight, insufficiently tested. When clogged sufficiently the combustion chambers overheat (due to insufficient exhaust gas, which has less oxygen, is less combustible). This leads to head gasket failure, which typically involves coolant leaking into the combustion changers. The leaking coolant tends to accumulate as the car sits overnight, and so cold start in the morning are the worst. The pistons struggle with the (uncompressible) coolant, the damper (aka "flywheel")between the engine and transaxle is stressed, can break springs, and so on.

The immediate "fix" is head gasket replacement, If it's not so far gone that the head or block are warped, and/or a piston arm is bent.

I would replace the water pump too; they have a plastic impeller, that has a lifespan of around 150K miles tops.

To prevent a another blown head gasket, clean the full EGR system (see top two links in my signature; on a phone turn it landscape to see signatures).