Ok, so hear me out. If you are going to use a Rock or a Ground type, Tyranitar is your best option. Sand Stream boosts its Special Defense by 50%, so I wouldn’t be as worried about Red’s team. If you can outspeed Lapras, a super effective Stone Edge (level 54 as a Pupitar)/Rock Slide (level 14 as a Larvitar) should do the trick. Earthquake (level 47 for Pupitar) should take care of Pikachu (watch out for Iron Tail, though it might miss). For Venasaur you can bring Tyranitar to the Move Tutor to teach it Fire Punch. Thunder Punch can go into the last slot for Blastoise. Note that this set has no Dark STAB. If I were to put the set together, it would look like this:
Tyranitar @ Expert Belt (Mount Silver)
Ability: Sand Stream
- Fire Punch
- Stone Edge / Rock Slide
- Thunder Punch
The set has plenty of coverage, so I feel that the Expert Belt works great with it. Like I said, these moves can destroy Red’s team. Stone Edge/Rock Slide are 4x effective against Charizard, and Thunder Punch is 2x effective on it. That’s 5 Pokémon taken care of in one set. Also, Snorlax has mediocre defense, so you could use this against Snorlax too.
The only downside to Tyranitar is that you can only obtain Larvitar at Mount Silver, so you can only really use it in the battle against Red since it’s so late game, where it is level 15-20. If you’re willing to grind though, I highly recommend Tyranitar.
Hope this helps! :)