Optical Rendering
The whole world is realistic due to real-time reflections and refractions!
Chemicals & Reactions
The whole periodic table of elements and their compounds are free to use (as exhaustive as possible), with all kinds of reactions and all kinds of effects:
Combustion, solution, precipitation...
Thermodynamics
Matters can change state according to temperature: ice, water, vapor...
Heat can transfer: different matters have different properties.