Boromir blunts its enters-the-battlefield trigger
For example, if an opponent controls Blood Moon, an enchantment which says "Nonbasic lands are Mountains," and you play Rootpath Purifier, Blood Moon can no longer apply to the lands you control because they are all basic
If you found yourself playing someone with a control deck (cards like Languish and Radiant Flames were our enemies), you could board into Needle Spires
This choice is made as the creature enters the battlefield, so no one can respond to the choice
You can see in my guidebook that it's in great condition, so much so that I actually removed it while writing this article, in the hope that it receives a high grade to add to my GB Promo collection
Though, it can be argued this is true in some regard with all card games, on or offline