This mod adds 2 new ores (Crimson, and Blacksteel) which are found between y levels 0 and 5. The Crimson and Blacksteel ores drop Crimson or Blacksteel shards depending on the ore. If you make a crusher machine ( 8 iron blocks surronding a piece of redstone) and put a Crimson shard into it, it will make a Crimson ingot. If you put 9 Blacksteel shards into a crafting table (not stacked) it will make a Blacksteel ingot. These 2 ingots can make different Crimson Weapons and armor.
There will be a crimson biome that can be found, and in that biome there can spawn a boss named Crimson Lord.