A greater degree than most. A level that cannot be beat. For example, to like the mostest would be the ultimate level of liking that cannot be surpassed.

More than most.

Mostest, when someone calls mostest there is nothing that can beat Mostest so if they say tie they can not tie the person who called it wins. Only one person can call it the first to call it wins NO MATTER what.

A word used by illiterate young persons expressing an over exaggeration of an opinion or fact; to the greatest power of most

Mostest is a childish way to win an argument. More than most.

The love that Ben has for Becky; which is greater than the love that Becky has for Ben