Ice types

Ice types are very useful when you're up against a dragon type. Dragon types are usually hard to KO but with these Ice types, Dragon types are also going to faint in one icy attack. Ice Beam is 4x effective against a Dragon and to add to that Ice Beam is 1.5x more effective because Ice Beam is an Ice move. All Ice types can learn Ice Beam, but look out for Fire and Fighting Types. Many Ice Types are also Water Types so Fire Type moves aren't as effective. (You can find Sneasel in the dark section)

Dewgong is a Water and Ice type that evolves from Seel. Seel can be found on Seafoam Islands in Pokemon LeafGreen/FireRed. Dewgong can learn Surf so it can launch a super effective attack on Pokemon like Charizard Dewgong can also be trained easily when battling trainer with Flying Pokemon. I would recommend the place to the left of Pewter City to train Dewgong(or Seel).

Lapras is also a Water and Ice type that has teh ability Water Absorb. Water Absorb is great when going against Water Types because all Water type moves are useless against Lapras. If Lapras is lacking some HP when battling and if your opponent uses Surf, Lapras will regain HP! Lapras can also use Psychic and is a perfect candidate for the Beauty Contests(Although Lapras can still win the Tough Contests. Drakyria has tried it before and her Lapras won the Master Rank Tough Contest).

Jynx is very hard to KO if you don't have a Fire or Fighting Type Pokemon. Jynx is a Psychic and Ice type Pokemon that can confuse and attract your Pokemon. Jynx has the potential to KO an opponent without it having to lose a single HP. Jynx is also hard to find but I'm pretty sure you can find one on Four Island in the Icefall Cave.