For full Forest Titan taming details, get the taming calculator app.
To tame a Forest Titan, you must destroy the corruption on its body. Taming effectiveness will drop if you hurt the Titan, so try to focus on the corruption. Titans come pre-equipped with a Platform Saddle, however, they are piloted from a seperate cockpit. Titans are a 24 hour temporary tame.
Pro tip: Don't use explosive weaponry and really bad rexes with no saddles like the devs did. Fab Snipers for taming it with little/no collateral damage, actually decent rexes + imprint + saddles to kill it
It is the best for raiding a high level base it can grab most enemies and kill them the ones that survive can be picked of by some rex's or gigas you brought add some rock golems to soak turret damage and you have an unstoppable Force