ground types will take care of zebstrika but her 2 emolga are immune to ground moves... so i suggest rock and ice type moves for those 2 emolga
it would be best to use ghost Pokemon against the gym leader
the 5th gym leader. ground type master Clay (would have been useful against him!)
Not that I know of... Unfortunately.... They sure would make a great place to train, wouldn't they?
The fifth gym leader Koga uses Poison type pokemon so your best bet is to use Psychic or Ground types against them. A Kadabra(Alakazam would be even better) can easily take care of all of Koga's pokemon.
The fifth gym leader is actually in an old town that you had visited previously. The fifth gym leader is Norman in Petalburg city. In order to beat him I would bring a good Pokemon with good fighting moves, otherwise you wouldn't survive against Slaking or Vigoroth.
If you can find an electric, ice or rock Pokemon anywhere, then that's good. A normal, fire, water, poison, flying, psychic, ghost, dragon, dark or steel Pokemon is okay. A grass, fighting or bug Pokemon will do bad. A ground Pokemon will do HORRIBLE! I beat her with a high level grass Pokemon (Serperior), but I would suggest using a different type! I hope I helped you! :D Against her Swoobat, you should not use a psychic Pokemon, and against her Swanna you should not use a water Pokemon.
no that would be cool but no
That would be Landourus.
fighting types moves are great against her but her miltank has a great defense so it would be better to hit it with a strong special attack
Ground types are great against electric types so find yourself a decent ground type Pokemon and train it a bit then use it.
luxary
In Pokemon HeartGold, the 6th Gym Leader is Jasmine in Olivine City. She uses Steel Pokemon in her party, and more specifically uses 2 Magnemites and 1 Steelix. The best type to use against the Magnemites would be Ground, as that would be a doubly super-effective move. Fire and Fighting moves will also work here. Against the Steelix, Fighting, Ground, Fire, or Water moves would be super-effective. Be warned, though, that the Steelix has the move Rock Slide, which will super-effect a Fire Pokemon.