HeartGold Team...

[Star Champion AJ]

I decided to restart HeartGold...
1) For that playthrough I plan to use only Gen II Pokémon.
2) This in-game team is only for the first part of the game (the 8 Johto Badges+Elite 4). I'll add the team for the second part (the 8 Kanto Badges+Red) later.
3) Also Natures, EVs and held items will not be considered, only the Abilities and Moves.


Ability: Blaze
Flamethrower
Headbutt
Shadow Claw
Rollout

The starter and the best Fire-type available since there aren't any decent Gen II Fire-types, besides Houndoom which is post game, I can't trade Magmar and Arcanine can't be used due to the Gen II only rule.
Note: Focus Blast's accuracy is too low to be useful ingame.


Ability: Serene Grace
Fly
Flamethrower
Extrasensory
Magical Leaf

One of my favourite Gen II Pokémon and it's available early, thanks to a Kinomo Girl.
Since the Shiny Stone isn't available before facing the Elite 4 and therefore I can't get Togekiss, Togetic will be my Flyer.


Ability: Static
Thunderbolt
Fire Punch
Signal Beam
Thunder Wave

Electric-types are useful mainly against Water-types and Falkner is dead meat because Mareep is available before the Gym Match.


Ability: Water Absorb
Earthquake
Surf (just a filler)
Waterfall
Return

Emeraldfan suggested a physical based Water or physical based Grass type and the best choice was Quagsire, though it shares a Grass-type weakness with Mamoswine, Typhlosion and to a certain extent Ampharos can cover the Grass-type weakness very well.
And something says I'll like Quagsire's derpish face...


Ability: Synchronize
Psybeam
Bite
Swift
Reflect

Another gift Pokémon and my favourite Eeveelution.
Well... its moveset is crappy since I have no access to most useful moves (either TMs and Move Tutors).


Ability: Oblivious
Earthquake
Ice Fang
Ice Shard
Return

Though it's available a little late (after the 7th Gym and the Team Rocket events), I know a powerhouse when I see one and Dragon-types won't stand a chance against Mamoswine.
The double Ice STAB depends of how faster (Ice Shard) or slower (Ice Fang) my opponents are than Mamoswine.

[Emeraldfan]

Allright. For now I do assume that this is all just planning? Because that means we can suggest natures.

Typhlosion
Hasty / Naive
~ Flamethrower
~ Eruption
~ Return
~ Focus Blast

You should be able to get all of those TM's needed both before the E4 and multiple times.

For Togetic, I'd recommend a Mild nature and I also advise replacing either Magical Leaf or Ancientpower with Flamethrower.

Ampharos
Modest / Mild
~ Discharge
~ Signal Beam
~ Focus Blast / Fire Punch
~ Thunder Wave

If you decide not to run Fire Punch, go with a Modest nature. Otherwise pick Mild.

Espeon
Timid
~ Psychic
~ Swift
~ Morning Sun
~ Psybeam

There is not much Espeon can learn, and after removing all the moves that cannot be learned in the first part of the game, there's almost nothing to work with. Psybeam is a filler move here, but might help out PP-wise.

Mamoswine
Adamant
~ Ice Shard
~ Ice Fang
~ Earthquake
~ Return

Double STAB, and Return is the best move available to you.

For you last pokemon, I'd advise a physical based Water or physical based Grass type.

[Star Champion AJ]

Allright. For now I do assume that this is all just planning? Because that means we can suggest natures.

For you last pokemon, I'd advise a physical based Water or physical based Grass type.

That's right, this is just planning, however the Natures will come naturally as long as it isn't a hindering one.
Considering the Gen II only rule I self-imposed, the best choice for a sixth Pokémon based on your opinion would be Quagsire... a Pokémon I never trained before (maybe it's because of its derpy face), available early, however it shares a Grass weakness with Mamoswine, but that's covered by Typhlosion and to a certain extent, Ampharos so anyway, it's a good choice.

Anyway there's a moveset for Quagsire

Earthquake
Surf (just a filler and I lack a Surfer)
Waterfall
Return

Note: Typhlosion and Espeon's movesets require too high levels for the first part of the game (Level range between 45-50) and I usually don't level grind and everybody knows that HGSS has a terrible level curve.