Without Controlfile!!

Is it possible to start the instance if the Controlfile is Lost or got corrupted...

No, but if you have mirrored copy you can.
If you dont have any then you could recrete the controlfile and start the database

I think there is one possibility of mounting the instance for creating the controlfile.. i.e. by changing the value of INIT Parameter.

I am curious to know, if you could recollect or point to the source where it has been mentioned.

If not all control lost, instance can still be started, but cannot use database.

I dont see very clear your point wreno, you can always start an instance without a control file since the instance is started in nomount state and control file is read in mount state (instance is started before control file comes into play), actually to create or recreate a control file you first start an instance to do it

I think you can make a

alter database backup controlfile to trace

if the database is not mounted, you then resolve the problem by recreating your control file ...

If the database is not mounted then the database has no idea what is the content of the controlfile and thus you can't isue BACKUP CONTROLFILE TO TRACE!

What happens (regarding init, control, log and data files) during each startup phase:

1. NOMOUNT: Instance reads the init.ora (this file also specifies where the instance should look for the control files)

2. MOUNT: Instance opens and locks the controlfiles, specified in the init.ora (controlfile includes all informations regarding redolog and database files)

3. OPEN: Instance reads and locks all redologs and database files and makes the database available for users.

So you must be at lest in the MOUNT mode to get the information contained in controlfile.