Best time to enter Battle Mountain?

[dreizehnX]

At first I thought Battle Mountain is some kind of bonus area, then I thought I'd go there just before going to fight the final boss.
Then I stumbled across the fact you can find more summons at Battle Mountain.
So I guess is it not only a bonus area.

Now I am 1 screen away from the final battle and I still haven't visited Battle Mountain.

Was this a bad decision? Is there even a 'best time' to visit Battle Mountain?
Can you also please tell me how many and which summons I can find there? I have only 21 so far and finding 5 summons there sounds a bit unbelievably to me .

[ɹǝǝpᴉnbS™]

Your best time really is as you progress through the game. If you wait until just before God Cat, A majority of the gear isn't going to see any playtime.

[Rocket2049]

if you're playing epic difficulty it's probably a good idea to go through all of it now, but leave the marathon battles for later since there's no reward for finishing them.
and yes battle mountain is a bonus area, it wasn't in the flash game originally, you're in no way forced to play through it.
pretty much battle mountain gives you all the premium stuff you had to pay for in the flash game
you can definitely wreck godcat without ever touching battle mountain

as for summons I know you get cosmic monolith which is the strongest summon (with the highest cost to use of course)

[dreizehnX]

Thanks for that. ^^ Of course I'm mostly curious about this area and... I also want to unlock all of the achievements. As this is finally a game with realistic ones as far as I see