PC How to stop the spread of the crimson biome?

[Oofio19]

I just advanced to hardmode and realised: "I didn't block off the crimson biome!" And now i fear im in big trouble, i can't to dig around it now because of all the mobs!
What should i do? Is there still a way, or do i need to start a new world?
Also i am a Mage, i like the damage but defense is very poor, im thinkig of switching to ranger.

 

[Dapling]

You can dig a trench around everything you think is important (your base) instead of around the entire crimson. There's also an NPC which moves in once you have killed any hardmode boss which sells an item that can help destroy the Crimson.

 

[Oofio19]

You can dig a trench around everything you think is important (your base) instead of around the entire crimson. There's also an NPC which moves in once you have killed any hardmode boss which sells an item that can help destroy the Crimson.

Thank you!