As the 2nd true flip Planeswalker on both sides (Garruk Relentless into Garruk, the Veil-Cursed was the first), Arlinn offers a lot of options
The second you have two or more of these, your opponent needs cards like Tragic Slip to get around them
You can also add more counters using Skrelvs activated ability, which can be activated multiple times a turn if you include ways to untap creatures or artifacts
A Selesnya Planeswalker deck would have access to several Ajani-adjacent cards, each of which offer a nice bolstering effect to your cards
Now, if you have Seeker of Skybreak, you can attach the bow to it, and have it target itself to untap giving infinite ping damage, and winning you the game
You choose targets and deal three damage somewhere