The three are the top three flying Pokemon obtainable in HeartGold (In my opinion of course, some might argue that Delibird is quite good)
Crobat
Movesets: For Crobat you can use the sets I posted here
Locations obtainable(As its pre-evo Golbat):
- Mt.Mortar
- Whirl Islands
- Victory Road
- Safari Zone
The biggest problem with catching Golbat, and almost any Pokemon, at such a late stage in the game, is that it can be quite difficult to level them up for battling standards. So my suggestion would be to avoid as many trainers as possible before Victory Road, catch your Golbat, then go back and battle said trainers.
Evolution: Happiness
At such a late level it can be quite difficult to level him up enough to like you. For that reason I would suggest catching a low level Zubat, then going and battling higher leveled wild Pokemon, he'll like you more and it won't be too much extra time.
Xatu
Movesets:
Now generally for in-game you'd like an offensive moveset. This tends to be the way of the game so i'll post some offensive sets here.
Xatu @ Leftovers/Life Orb
Trait: Synchronize
EVs: 252 SAtk / 252 Spd / 4 HP
Modest Nature
- Psychic (Level-up)
- Shadow Ball (TM)
- Giga Drain (TM)
- Roost (TM)
Mostly TM moves, so I hope that's not a problem.
Xatu @ (Whatever really)
Trait: Synchronize
EVs: 252 SATk / 252 Spd / 4 HP
Modest Nature
- Heat Wave (Move Tutor)
- Psychic (Level-up)
- Signal Beam (Move Tutor)
- Shadow Ball (TM)
In-game movesets tend to have whatever item and no EVs so you can disregard those if you wish. Otherwise these two sets are what I would go for in-game. You could also just throw Fly in there instead of any of those moves.
Locations: Rout 28, Ruins of Alph, Mt.Silver (all as Natu)
Evolution: Level 25
Gliscor
Movesets: In-game you'll want to run a physical moveset, here's my suggestion,
Gliscor @ (Again in-game doesn't really matter)
Trait: Hyper Cutter
EVs: 252 Atk / 252 Spd / 4 HP
Adamant Nature
- Earthquake (TM)
- Night Slash (Level-up)
- Swords Dance (Level-up)
- Steel Wing/Stone Edge (Both TMs)
Physical in-game sweeper. Stone Edge > Steel Wing unless you have another poke you want to learn Stone Edge.
Locations Obtainable: Route 45 (As Gligar)
Evolution: Level up at nighttime holding Razor Fang
Razor Fang can be obtained at the Battle Frontier.
Which is after the main game so I kinda wished i'd checked that first xP
Anyway you've already selected BA but I decided to finish as I was almost done anyway.