How the heck are you supposed to make it Red if you can't beat Bugsy? That makes as much sense as a grilled cheese sandwich without any cheese lol
In some solos, you'll have a hard time in some early fight, then have it easier until much later.
By the time you fight Bugsy in a Meganium solo, you're a Bayleef whose only non-Grass attacking move is Tackle. You could upgrade to Cut for slightly more damage, but that can't be deleted until Blackthorn City. Grinding is also annoying in Crystal once you run out of trainer battles because everything has low levels. Scyther has high stats for this point in the game, and Fury Cutter hurts when it's both super effective and gets stronger for each consecutive hit. Eventually, you may get lucky with critical hit Tackles or Fury Cutter misses. Perhaps Poisonpowder, Synthesis, or Reflect could be used.
When you beat Bugsy, the game gets easier for a while. Bayleef can get the Return TM in Goldenrod City and pretend to be a Normal type when Razor Leaf is ineffective. Chances are you'll evolve into Meganium right before you reach Ecruteak. You'll want to hang on to Mud Slap for Morty's Gastly line and Jasmine's Magnemites.
You'll find Earthquake in Victory Road, which helps Meganium deal with Magneton, Typhlosion, Gengar, and other Pokemon it previously had trouble with. Just in time for the last Johto rival fight!
Karen and Lance are the next big hurdles for Meganium. Karen's Umbreon knows Sand Attack and Confuse Ray to trip you up. Vileplume can use Stun Spore to slow you down, making you susceptible to Houndoom's Flamethrower. Lance has a Charizard and Dragonites with moves like Thunder Wave and Fire Blast.
Most of Kanto is a joke in Crystal solos because most of the Gym Leaders' Pokemon are lower level than Lance. (Janine is weaker than Clair, even!)
The reason Red is so hard for Meganium is that he has a level 77 Charizard. Your level advantage is mostly gone by the final battle. Even Meganium's decent defensive stats can't save you from Flamethrower, and a critical will kill you outright. My solo Meganium had to level up to 84 to have a chance to 2HKO Charizard with Return, and even then victory wasn't guaranteed.
EDIT: I should mention that Rest and Sleep Talk are your friends. Even if you're not using them for the rest of the playthrough, consider this combo for the Red fight.