I want to transfer a Pokemon from my Pokemon Black game on Twilight Menu to Pokemon Bank, is that possible somehow? The only solution I could find was transferring the Pokemon through PKHeX but I don't have access to a computer at the moment.
Do you have any of the 6th or 7th gen Pokemon games? If so, you could use the homebrew app Pokemon PKSM to transfer the pokemon from your digital copy of Pokemon Black saved on your SD card to one of the 6th or 7th gen games. From there, you can transfer those Pokemon you traded from your copy of Black to the 6th or 7th gen game into Bank.
In fact, PKSM can be used this way for getting Pokemon from as far back as Gen 3 into Bank. And then Poke Transporter can of course officially be used for digital copies of the Gen 1 and 2 games to get those Pokemon into Pokemon Bank. It's pretty awesome how the first 7 gens of Pokemon can not only be played on a 3DS, but with the right homebrew and official apps, all the Pokemon you get in all those games can be transferred to the Pokemon Bank.