More thoughts on this idea.
Mobs by biome. Polar bears and seals in snow biomes. Scorpions and camels in desert biomes.
Thirst mechanic. Ocean water = salt water and not thirst quenching. River water drinkable, but contaminated, so some disease damage as a result. Add filtration methods, and other drinks as options.
Temperature mechanic. Different biomes have different temperatures. Wearing your iron/diamond armor in the desert makes you too hot, and you become thirsty much, much faster. Wearing lighter clothing, a large brimmed hat or head scarf would help keep thirst down. Similarly, dress warmly for a colder biome or take freezing damage. Using animal pelts to create heavy coats/parkas to prevent this.