The IBiome interface allows you to retrieve information on a registered Biome.

It might be required for you to import the package if you encounter any issues (like casting an Array), so better be safe than sorry and add the import.
import crafttweaker.world.IBiome;

You can get a list of all registered Biomes using game.biomes from IGame

Atm, all you can do with an IBiome object is retrieving some information out of it:

ZenGetter	Return Type
ZenGetter name	Return Type string
ZenGetter canRain	Return Type boolean
ZenGetter isSnowyBiome	Return Type boolean
ZenGetter highHumidity	Return Type boolean
ZenGetter spawningChance	Return Type float
ZenGetter baseHeight	Return Type float
ZenGetter heightVariation	Return Type float
ZenGetter rainfall	Return Type float
ZenGetter waterColorMultiplier	Return Type int
ZenGetter ignorePlayerSpawnSuitability	Return Type boolean
ZenGetter temperature	Return Type float
ZenGetter types	Return Type List<IBiomeType