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