Before any 3D monsters, we built a tiny version of the game in a web browser in a couple of days. A lobby with three portals, one map, blocky monsters and a results screen. It looked rough on purpose.
A first version has one job: to answer a question as fast as possible. Ours was, is this fun? Hiding was fun. Running was scary. That was enough to keep going. Game makers call this an MVP, a minimum viable product.
Then came the real build. This week the first beta went to a small group of family and friends. It has two maps, four monsters, a secret lab, Benjamin's Infinity mode, and you can play together over the internet. The first test was two computers in two different rooms, and it worked.
Then the bugs arrived, which is the point of a beta. Rescuing a caught friend didn't work. One player froze in the water. The nights were too dark. Thirsty was too good at his job. We fixed those, and the testers found more. That's how it goes.
What we learned: build the smallest thing first, give it to real people early, and write down everything that goes wrong. There's more on the How we work page.