Are you only going to use four Pokes in battles with your friends, or have you just not thought of two others yet? Also, how do your friends battle? Do they subscribe to the strategy of battling the AI, where it is all about attacking or do they understand the true strategy of battling that requires switching out and prediction? I will assume the former, since your team is based on that same premise. I will do my best to educate you on the latter, to give you an advantage over them.
My Leaf Green team
Charizard
Trait: Blaze
Gentle Nature
-Wing Attack
-Earthquake
-Flamethrower
-Iron Tail
First off, I wouldn't use Charizard at all. Fire-types, especially Charizard, had their moment in the sun back in RBY, but now there are just too many counters to exploit their weaknesses and bad defenses for them to be effective. Personally, I would suggest your lead Poke be a physical attacker that is fast and that can damage the most types. Since this is LG and you don't have access to Salamence, I would go with Aerodactyl:
Aerodactyl @ Choice Band
Trait: Rock Head
EVs: 4 HP / 252 Atk / 252 Spd
IVs: Max Atk and Spd
Jolly Nature (+Spd, -SAtk)
- Aerial Ace
- Double-Edge
- Earthquake
- Rock Slide
This is your "Hit & Run" Poke. Cause serious damage and then switch out. Double-Edge takes advantage of its Rock Head Trait that prevents any recoil while dealing good damage to the opponent. Aerial Ace is a STAB attack that will never miss. Rock Slide is another STAB that can cause the opponent to flinch, which is extremely beneficial to Aerodactyl. Earthquake is for those Rock/Steel-types that resist its other moves. This is a terrific opener and late-game cleaner.
Raichu
Trait: Static
Naive Nature
-Thunderbolt
-Substitute
-Focus Punch
-Thunderwave
If you are going to use a legendary bird, I would use Zapdos over Articuno, especially a Jolly Articuno. Zapdos outclasses Raichu and has that very nice Ground immunity:
Zapdos @ Leftovers
Trait: Pressure
EVs: 60 HP / 76 Def / 144 Spd / 96 SAtk / 116 SDef
IVs: Inapplicable
Modest Nature (+SAtk, -Atk)
- Drill Peck
- Light Screen
- Thunder Wave
- Thunderbolt
Not necessarily your second Poke, but I figured it would do good to replace Raichu. While Zapdos does just fine on its own, it is at its best when a Sub is passed to it, so it can use its speed and power to sweep through your opponents. Despite the -Atk nature, a STAB Drill Peck still does great damage. Light Screen not only protects it from Ice attacks, but also protects your team against special attacks in general. Thunder Wave is a great status inflicting move. Speed over your opponent is an important strategy when competitive battling, and the 50% parahax is nice too. A STAB Thunderbolt from its its great base SAtk (125) doesn't hurt either.
Snorlax @ Leftovers
Trait: Thick Fat
EVs: 160 HP / 136 Atk / 136 Def / 76 SDef
IVs: Max HP, Atk, and SDef
Careful Nature (+SDef, -SAtk)
-Shadow Ball
-Body Slam/ Return
-Rest
-Sleep Talk
EXCELLENT choice, HORRIBLE nature. Breed that one over please. Stalkerlax not only is a good special wall (switch this in against special attackers), but it can hit back physically (which most special attackers are weak against) and Rest off any status/HP loss and continue to pound the opponent with Sleep Talk. While Body Slam has that sexy parahax, Return hits harder. I would actually suggest Double-Edge, but you are using that on Aerodactyl. Snorlax usually brings out a Fighting-type counter that you can handle with Zapdos quite easily.
Articuno
Trait: Pressure
Jolly Nature
-Ice Beam
-Aerial Ace
-Water Pulse
-Mist
With Zapdos in place, this leaves a spot open for Vaporeon:
Vaporeon @ Leftovers
Trait: Water Absorb
EVs: 222 HP / 176 Def / 16 SAtk / 96 SDef
Bold Nature (+Def, -Atk)
- Baton Pass
- Substitute
- Surf / Ice Beam
- Wish
More often than not, this will be your second Poke. A novice trainer will see Aerodactyl and instantly decide to bring in a Water-type. What better strategy than to switch in a Water-type of your own? Your opponent will either have to switch out or attack with weak attacks that Vaporeon can easily handle. Either way, you are now able to set up. Vaporeon creates the strongest Subs in the game. Put one up immediately and you can attack behind it, or use Baton Pass to pass its strong Sub to a teammate (i.e. Zapdos). Wish is also EXTREMELY helpful as it not only heals Vaporeon itself, but can heal its teammates too. Surf or Ice Beam is your preference. Personally, I would prefer a STAB Surf that reaches more types than Ice Beam does.
Comments and critism welcome, I'm trying to assemble the best team possible that I can battle my friends with
The fifth spot should go to a versatile special attacker. There are two LG Pokes that instantly spring to mind - Alakazam and Gengar. While Alakazam is the better special attacker (with a STAB Psychic attack), Gengar has better intangibles. It has Levitate, and is immune to Normal and Fighting attacks. Either would be an excellent addition to your team:
Alazakam @ Leftovers / Lum Berry / Choice Band
Trait: Synchronize
EVs: 4 HP / 252 Spd / 252 SAtk
IVs: Max Spd and SAtk
- Calm Mind / Encore / Trick / Ice Punch
- Fire Punch
- Psychic
- Thunderpunch / Ice Punch
Alakazam is extremely versatile. Encore is used on an opponent that likes to use non-attacking moves. Use Encore to lock them into that move and proceed to set up yourself. Trick is for an opponent that likes to abuse Blissey. Take that Leftovers away from it and then proceed to wear it out with Alakazam or switch to a more appropriate counter. The other strategy is just a straight up power sweep. Either four attacks or abuse Calm Mind behind a Sub from Vaporeon. Deadly.
Gengar @ Leftovers
Trait: Levitate
EVs: 108 HP / 188 Spd / 212 SAtk
IVs: Max Spd and SAtk
Modest Nature (+SAtk, -Atk)
- Hypnosis / Will-O-Wisp / Focus Punch
- Fire Punch
- Ice Punch / Giga Drain
- Thunderbolt
Too many options to really list here. The first slot is total preference. All of them can be used by themselves or even behind a passed Sub from Vaporeon. Hypnosis, while not accurate, is great to have on your team. WOW is great to counter physical attackers. Not only does it Burn them, but also cuts their Atk in HALF. Focus Punch allows Gengar to surprise switch ins an Normal types that aren't smart enough to switch out.
The last slot will also be your preference. You can include another strong physical attacker or more of a utility Poke. I will cover both:
Tyranitar @ Leftovers
Trait: Sand Stream
Tyranitar @ Leftovers
EVs: 252 HP / 88 Atk / 168 Spd
IVs: Max HP, Atk, and Spd
Adamant Nature (+Atk, -SAtk)
- Dragon Dance
- Earthquake / Focus Punch
- Rock Slide
- Taunt / Crunch
DDtar is a complete beast than can sweep up easily late in the game, especially if it can Dragon Dance behind a Sub from Vaporeon. Earthquake or Focus Punch is your preference. Not many Pokes like a STAB Rock Slide from Tyranitar, especially DD'd one. Taunt prevents Tyranitar from getting statused as it sets up (if it doesn't get a Sub passed), but a STAB Crunch also ruins a lot of Pokes. I would use Naughty if you go with Crunch though.
Forretress @ Leftovers
Trait: Sturdy
EVs: 252 HP / 192 Def / 64 SDef
Impish Nature (+Def, -SAtk)
- Earthquake
- Explosion / Rest
- Rapid Spin
- Spikes
If your opponent likes to use Spikes, or even if they don't, Forretress can be useful here. It is one of only three Pokes that have both Spikes and Rapid Spin. The advantage Forretress has is its typing, excellent base Def (140), and its resistances. Explosion or Rest is your preference. Once three Spikes are up and you have no need for Rapid Spin, you can go BOOM against an opponent, or use Rest and keep this as a solid physical tank. Too many trainers discount the effectiveness of Spikes. Losing up to 25% HP every time a Poke switches in (not a Flying-type or Levitate Poke) can be devastating to a team, especially if you had Roar/Whirlwind on this team. To be honest, Skarmory would work very well with this team if you used that instead of Aerodactyl and went with Tyranitar.
Overall, you have a team with few shared weaknesses, but a lot of resistances. Good luck.