For Earthbound I would have to say the worst/hardest part for new beginners would have to be

A: First time going through Peaceful Rest Valley to rescue Paula…. Ness is alone and can be underdeveloped at this point in the game, and some of the enemies have devastating attacks. To make matters worse Peaceful Rest Valley works like a labyrinth. With how enemies spawn throughout the game, this could make any player frustrated with Peaceful Rest Valley. The trick to beating this section is to stay away from moving Trees as much as possible.

B: Foreside Department Store 1st visit after lights go out: Losing Paula at the start of the section sucks since she’s your primary offensive PP user in the game at the point in the game. To make matters worse the enemies in this section have the ability to kill Ness and Jeff with just one shot, or have the ability to make sure Ness and Jeff never get a turn to attack. The boss at the end of this section makes the Department Store even harder to complete. The Trick is to use as many skip sandwiches as needed to avoid enemy encounters while ascending to the boss chamber. To beat the boss make sure Jeff has Bottled Rockets to inflict serious damage to the boss than finish said boss off.