Forrest is great. Don’t think there is much sneaky stuff out there though as the trail network is well established and well looked after. Mariners run is my favourite out there, but other great ones include ‘follow the dog’ and ‘The red carpet’ descent. There should be good maps online for the You Yangs also. I’ve only ridden there once for a race last year. THe stockyards section is fast, flat and flowy, the rest is rocky and steep in places.
The comm games track and the rest of Lysterfield is fun although it gets a bit crowded and the trails do suffer a bit because of it. Check if the trails are open online. We were there a week ago and a few trails were closed due to water damage, but a number were open.
There are lots of other places to ride out this way also. Drop me an email if you want more info or someone to take you out for a ride. School hols at the moment so as a teacher I get to relax and look after my kids.