Azu
Retinazer
-Corruptors should regain their corruptive spit. This was a really unique ability of the Corruption, once it grew near the Player's domain, The Corruptors would make things even more difficult, and would at all times work to make it spread even further, only thick barricades could shut it out. It was removed in 1.2 as it was considered overpowered, but with the implementation of the Clentaminator I beg to differ.
-The Crimson should feature a new liquid, Ichor, that upon impact with blocks spreads Crimson, set it into motion and it will pour out over surfaces and convert everything in its path. Similar in physics to honeyblocks, destroying Crimstone has a chance of letting go of about half a bucket worth of this liquid. Breaking pots has this effect as well. - Firing random shots into the dark, or trying to mine away the Crimson would therefore NOT be very smart moves, as it may just spread even further by you doing so. Purification Powder and Clentaminator is the way to go. Touching ichor will inflict the Ichor-debuff, and will therefore become one of the major hazards discussed later on.
-The Burrowers, both Rotted and Normal would spread Contagious spores upon death, converting a small area of a few blocks where they die to Contagion. Waging wars against the Contagion outside of its own domain will be a futile effort since the more you slay, the further it spreads. (Minor reference to Gibli Studios' Nausicäe) Dealing with the mobs inside quarantines or within the biome itself would therefore be a more recommended approach.
No. The reason Corruptors lost this ability was because they could easily follow you back from anywhere and continue firing at you, making anywhere you go and more vulnerable to Corruption. I had one follow me back from the Ocean to my base in the middle of a large world just to corrupt it. Destroyer came and my town turned into an uninhabitable wasteland.There would be a special kind of mushroom in the Contagion, similar in shape to the Mushroom workbench, two blocks wide, but with a distinct appearance. When stepping on it it explodes dealing moderate damage, but also releases a cloud of spores. If you are unlucky enough to be hit by these spores you will get a debuff inflicted upon you, Contamination. This debuff covers your characters in spore-particles and makes the player themself temporarily spread Contagion wherever they go, binding the player to the Mires as long as the debuff lasts. (Want suggestions regarding how long this debuff should last, thinking maybe 2 mins).
All these mechanics don't add challenge or fun to the game, just tedium. Taking care of biome spread would be even more of a chore than it is now.