Any +1/+1 counters put on Raging Ravine remain on it even after it stops being a creature. They’ll have no effect until it becomes a creature again. (In other words, the land continues to rage, but to no effect.)

If Raging Ravine’s last ability is activated multiple times in a turn, it will get that many instances of the granted triggered ability. For example, if you activate Raging Ravine’s last ability twice and then attack with it, you’ll put a +1/+1 counter on it twice.

If this land becomes a creature but you haven’t controlled it continuously since your most recent turn began, you won’t be able to activate its mana ability or attack with it that turn.