if i want to kill the boss without any energy refiller or things that can refill our energy,is it possible to reach the boss stage?
boss of stages
Yes, it's more than possible.
The current [easily accessible, and by that, I mean no Shadow Key or something similar to the shadow key] would be Vanaduke. Assuming you start at the very first level of T3, you don't use too many revs, and you have 100 mist; you should be able to reach him using 90 mist. The other bosses, much less energy is needed for reaching them from the start of the tier to the boss it's self.
Heck, you can even have more mist leftover if you start at the terminal of each gate(By joining a friend or guild mate[If they allow it.] and you can still get around 3-4 tokens. It's also good, because you can avoid the odd stratums' weak crown pay off.[Odd stratums give out much less crowns then even stratums. And the difference is fairly big.) Of course, you should probably do the same for your friends too every now and then, so you don't leach them constantly.
Is that what you wanted to know?
If you're good enough to not waste all your energy yes.
in fact you have to be very bad to not reach the boss starting the day with a full tank. just dont waste energy on revives