Answer:
What do you call a pig that is no fun to be around?
I come with a train and go with a train and the train doesn't need me but can't go without me.
Adored by few, feared and hated by many. Mistress of the entire universal reason, master in the art of numbers. Some may have solved many of my mysteries, but there are still many of them to find. What am I?
I am a vegetable that bugs stay away from
Light me up in backyard gatherings
Give it food and it will live, give it water and it will die.