LRM-00101: unknown parameter name '_first_spare_parameter'
From the spfile create a pfile, which can be edited directly:

sqlplus / as sysdba
create pfile='/tmp/pfile.ora' from spfile;
exit


Edit /tmp/pfile.ora, remove _first_spare_parameter. Then create the spfile again:

sqlplus / as sysdba
create spfile from pfile='/tmp/pfile.ora';


Now you can try starting your instance.

Above should work in a standard single instance environment, in a customized or clustered environment you may need extra steps.