While in Team Fortress Classic, become a spy. Press
[Ctrl] to crouch. Press [Right Click] (special ability)
and select "Feign". If done correctly, you will have
feigned like normal, but instead of being on the surface, you
are now under it and are not visible by any other players. Once
you want to get out of this position, just stop "Feign".
Note: This is a good trick to do in an enemy's base, as you are
able to communicate with your team. This is also a good time to
change disguises, while no one can see you.
Strategy: Part 1: by James Spairana
Strategy: Part 2: by James Spairana
Strategy: by Matt Beisser