Here is the full list of all 9 Welcome Back achievements.
"You seem so wise all of a sudden haha!"
"I missed you so much..."
"I'm sure you were blessed by something"
"You're goint to grow strong and happy!"
"You went high enough, I guess"
"Literally High FIVE now"
"Pretty good aim with those four eyes"
"Oops, you don't have hands..."
"Okay, you suck! And also Spit!"