The function of the substantia nigra pertains to the control of eye movement, motor planning and reward seeking.

It is easy to remember the name and function of this brain area using this mnemonic:

Planning on going to the Nigra Falls to see the substantial amount of water that falls aswell as to gamble and win money.

The name of this brain area is remembered through the words nigra and substantial. The function of this brain area is encompassed in the remaining words that are underlined. 

Planning on going relates to the motor planning aspect of the substantia nigra.

Seeing the water relates to eye movement.

Finally, because nigra sounds similar to Niagara, we can assume there are many casinos and there will be gambling, which suggests winning money, which would be reward seeking.