"without paying your mana cost" is well worth remembering here
As a game goes on, one of my favorite ways to use Weathered Wayfarer is to find lands that can help keep my land count just under the player with the highest while still advancing my mana or other agendas
The fun really begins when Asmo hits the battlefield, as you can tutor for The Underworld Cookbook
In Commander, this card isn't quite as strong, since you only have one copy, but wow is this card really punishing
Blue mind controls rarely grant haste, so the stolen creature is unable to attack the turn it switches controllers
I think this works especially well as a defensive card, as it can bait attacks from larger creatures only to then overpower them with an instant that boosts its stats, which also gives it first strike