Nidoking @ Choice specs/Expert belt/Life orb
Recommend nature: Modest
Recommend EV spread ( if you are into EV-training): 252 SpAtk, 126 HP, 126 Speed
- Flamethrower/Fire Blast
can actually get you through the battle tower. It OHKO's even before it reaches lv.75. You can always keep your Emboar since it is always fun conquering the Black tower with your trusty starter. Keldeo works great at the battle tower after you have had a theoretical view on it. It has great SpAtk. stat and Speed stat and is a monster in the black tower tower. If I would recommend such a Keldeo
Keldeo @ Life orb
Recommend Nature: Timid (+ speed, - attack)
EV spread: 252 SpAtk./ 252 Spe
-Aqua Jet ( trust me, you wouldn't want to be struck by Benga's Volcarona's psychic after one Quiver Dance
-Icy wind ( not the strongest ice type move, but it works great with Keldeo) Hidden Power Ice ( not very easy to get in-game, but if you are determined to get it, then go with this instead)
This is just a recommend Keldeo for the black tower, but any Keldeo could deal with the Battle Tower, as long as it doesn't lower it's SpAtk stat. I suggest you should try to double check if your Keldeo is: Brave, Adamant,...). A Modest or Timid Keldeo is perfect. Quiet is not what you are looking for on Keldeo since it lowers it's speed. Mild is ok and so is Rash.
tbh, you could beat the Black tower with any team. I did it with my in-game team ( Samurott, Flygon, Arcanine, Lucario, Unfezant and Magnezone) but they were all around lv. 79-82.
Hope this helped and good luck with your challenge :)