What sort of Pokemon is good for single-mon runs?

[johnny-walkers-butt]

I'm about to play my first single-mon run in Crystal and I'm wondering if anyone has some tips as to what makes a good choice or a bad choice. I'd really like to play Gastly-Haunter-Gengar, but I feel like that type coverage will be awful in the early game... Thanks!

 

[kaiomann]

In gen 1 the Abra line was amazing, don't know if it still applies in gen 2. Also the trade evolution could be a problem.

 

[Ｄｉｓ]

Furret. Just teach it Dig or Mud-slap to cover Morty and Jasmine.

 

[Fairy Ice Ricky]

For Gen II, Typhlosion and Feraligatr are good Pokémon due to their coverage (Flamethrower/Thunderpunch/Earthquake and Surf/Ice Punch/Earthquake, respectively) and fairly strong attack stats, and you don't need to worry about trading/waiting to get your planned 'mon since you get them from the very beginning. Abra is another really good Pokémon--uber-high Special Attack, and combined with Psychic + the Punches, you have many of your bases covered with a Kadabra (seriously, you don't need Alakazam).

In general, it's better to get fast & strong-hitting Pokémon since you can quickly roflstomp over your opponents before they can even get a chance to hit you.

 

[TEMMEC]

Hey! Are you looking to avoid using the starters as your 'single-mon?' Because I successfully ran through a game with just a Typhlosion as a kid (back when I literally only used Typhlosion). So that's an option.
In regards to Gastly-Haunter-Gengar: They would actually be overpowered in the early game. First off, they can get poison moves which obliterate all of the grass types that appear early game. Secondly, they are ghost type. Most of the attacks until the first or second gym are tackle and scratch; both normal type moves. There is the occasional water gun or absorb, but that is easily handled.
If you're looking for an out-there Pokemon that you've never really used before I would recommend a few.
1. Elekid-Electabuzz: Its only weakness is ground type and it has a fantastic move pool. It has thunderpunch, icepunch, firepunch, and it can learn things like dynamicpunch and rock smash for more coverage. The only weakness is his low defensive stats.
2. Rhyhorn-Rhydon: Very high in every useful stat except special defense and speed. It also has a 4x weakness to water which is very common. With a quick claw, though it can do work.
3. Onix-Steelix: If you were considering a Gengar, I assume you had some way to evolve it through trade. In which case, I will mention Steelix. This Pokemon is a monster. High attack, monster defense, fantastic typing, etc. It does, however have a mediocre special defense and a very low speed. But the speed doesn't matter much if you can take a single hit like a boss and then nuke them on the same turn. It also has a rather shallow movepool after it evolves so watch out.
4. Magikarp-Gyarados: Obviously you will need Magikarp to have some sort of attacking move off the bat and the early levels will probably suck, but Gyarados is worth it. He has fantastic stats all around, a huge attack stat, and a rather decent special defense stat. The only really sucky part is the fact that he is 4x weak to electricity.
5. Slowpoke-Slowbro: This one can be scary. Not 4x weak to anything, huge defense, huge special attack, decent hp and special defense. Fantastic movepool and huge type coverages: flamethrower (move tutor), icebeam (move tutor), psychic, surf, earthquake (is a physical move, though).
6.Growlithe-Arcanine: Fantastic, all around good stats. It has a rather underwhelming movepool, but it can be worked with. No fantastic type coverage, but if you flamethrower something, it's still gonna hurt.
7. Nidoran-Nidorino-Nidoking (My personal favorite): This one is controversial because his movepool sucks either way and he didn't get the ability that makes him viable until the next generation, but I love stomping on people who think that this monster is lame. I suppose you could go with the safer Nidoqueen, but all-in-all his attack stat is nothing to scoff at. He has some decent coverage considering there isnt a whole lot of psychic pokemon in this game until you fight Sabrina in Kanto.
Anyways, I hope you liked my list and I hope that I helped!

TEMMEC

 

[Karpi]

Ruby/Sapphire/Emerald - Swampert. I promise this is the easiest pokemon. RSE Swampert is one of the most overpowered in-game pokemon ever.

Diamond/Pearl/Platinum - Gyarados. Once you learn Dragon Dance you have already won the game. Just DD a few times at the beginning of a fight, heal him up, and I promise you will almost always win.

These are the most obvious and standout choices. I'm not really prepared to offer advice beyond that, but RSE Swampert and DPP Gyarados are basically pushing the limits of overpowered.