It's so annoying when a town is taken over by the Corruption or the Crimson, because the NPCs can't live there, and that makes the Pylons not work. So I'm suggesting a furniture item called the Purifier (better names accepted) that is sold by the Steampunker for 1 Platinum. It creates a bubble of purity that the Corruption/Corruption/Hallow can't take over. It's powered by Purifier Batteries, which are also bought from the Steampunker. There would be 3 tiers of Purifier Batteries, also bought from the Steampunker, and the first tier would be available at the same time as the Purifier. Higher tier batteries equal more battery life and larger bubble. Whenever the Corruption, Crimson or Hallow takes over a block inside the bubble, that block is purified and the battery loses a bit of its "life". When the battery runs out, the bubble disappears. The second tier would be available after Plantera, and the third tier would be available after defeating the Lunatic Cultist for the first time. Also, when you hover your cursor over the an active Purifier, it would display the percent of the battery life left.