[for those with paper journals, the entire post is written in over-sized letters with what looks to be either a very thick pencil or a massive crayon. for those using electronic devices, the entire post is in 32pt comic sans. that is also bright pink. it's rather impossible to say if the font choice and color was deliberate or not, even from a narrative perspective]
Dear Brand New Journal that Appeared out of Nowhere with a REALLY Big Key:
We're going to be bestest best friends. Well not bestest best because only Twilight and Applejack and Rainbow Dash and Fluttershy and Rarity and Gummy and Cherilee and Bon-Bon and Lyra and Ditzy and Dinky and Octavia and Big Mac and Scootaloo and Sweetie Bell and Apple Bloom and everyone else in Ponyville are my bestest best friends but we can still be friends don't worry.
Maybe you're a magical journal that lets me communicate with aliens from other worlds and the key that came with you goes in alien doors that lets me travel to those alien worlds* that would be REALLYNEAT. Please be that, new journal.
Your not quite bestestbest friend but still your friend, Pinkie Pie
*check with Twilight because Twilight knows things she's Princess Celestia's super duper smart favorite[favorite is smudged out in analog journals and struck through on digital ones such that it's still readable] only student after all