No, you don't need to be season 2+.
You start with X% chance of leveling them up. Everytime you pass that mission and they don't level, a few more percentage points are added to the chance.
sooner or later they'll finally level.
Being Season 2+ can make it easier, since there's a theme that increases the chance of leveling.
___________________________
"I've always wanted to be somebody, but I should have been more specific." - George Carlin
You start with X% chance of leveling them up. Everytime you pass that mission and they don't level, a few more percentage points are added to the chance.
sooner or later they'll finally level.
Being Season 2+ can make it easier, since there's a theme that increases the chance of leveling.
___________________________
"I've always wanted to be somebody, but I should have been more specific." - George Carlin