View all the monotype teams here: https://pastebin.com/S419KvS5
 
Pokemon Battle Tower Monotype team challenge
DARK team
Version: 2.0
 
H (Houndoom) @ Petaya Berry
Ability: Flash Fire
Level: 50
EVs: 4 HP / 252 SpA / 252 Spe
Timid nature  
IVs: 31 HP / 2 Atk / 31 Def / 30 SpA / 31 SpD / 31 Spe  
- Flamethrower
- Crunch
- Substitute
- Hidden Power [Grass]
 
U (Umbreon) @ Leftovers
Ability: Synchronize
Level: 50  
EVs: 252 HP / 252 Def / 4 Spe
Bold nature  
IVs: 31 HP / 0 Atk / 31 Def / 31 SpA / 31 SpD / 31 Spe  
- Toxic
- Psychic
- Wish
- Protect
 
S (Shiftry) @ Choice Band
Ability: Chlorophyll
Level: 50
EVs: 252 Atk / 4 Def / 252 Spe
Adamant nature  
IVs: 31 HP / 31 Atk / 31 Def / 30 SpA / 30 SpD / 31 Spe 
- Fake Out
- Brick Break
- Shadow Ball
- Explosion
 
Notes:
- Houndoom is a great Pokemon for early rounds because of its high Special Attack and dual STAB coverage, and it performs well in the late rounds because Psychic Pokemon are so common. Against Surf and Earthquake users, Umbreon can switch in easily and recover its lost health with Wish.
- Substitute works especially well on Houndoom since it 2HKOs nearly everything in the game with the Petaya Berry boost, and it needs the Substitute to survive a hit against many common moves.
- Despite this, Lum Berry + Fire Blast would be better on Houndoom if not for the Anabel 2 fight, where Houndoom needs the Petaya Berry boost to take down Raikou.
- Houndoom's Flash Fire ability can be quite effective against the AI. Since Houndoom has two possible abilities, the AI doesn't know it has Flash Fire until it activates. And since many Fire Pokemon run only Fire moves (or Fire is their best move against Houndoom), they'll often give you a free boost. 
- Like Blissey, Umbreon's all-around bulk and access to a healing move make it a pretty broken Pokemon in the Tower. The combination of Wish + Protect is as good as a standard healing move like Recover, and sometimes Wish can be timed to heal your HP (or your ally's) at a better time than Recover would. Toxic takes down everything except Poison types (hence the inclusion of Psychic), Steel types (easy for Houndoom), and Immunity Snorlax (2HKO'd by Shiftry Brick Break or OHKO'd by Explosion). The only moves that 2HKO Umbreon are Cross Chop (easily PP stalled with Houndoom's Substitute or Protect + Wish) and Megahorn (only found on Heracross, which Houndoom owns).
- Shiftry packs a punch with its Adamant nature + Choice Band, and Fake Out and Explosion compensate for its poor defensive typing. Fake Out can finish a Pokemon that Houndoom weakened, and it's often necessary against Reversal users. Explosion can OHKO Skarmory (!) and Snorlax after 2 Curses.