Normally when under the effects of Toxic ("Bad Poisoning"), your Pokemon takes incrementing amounts of damage: 1/16, 1/8, 3/16, and so on, of their max HP. You can negate this by switching out; when the Pokemon returns, it will only be taking a flat 1/8 damage like regular Poisoning.
Leech Seed is a move well-known for absorbing 1/16 of the target's HP and healing the user of the move by the same amount. However, you can actually boost this damage through the unintended effects of Toxic. When you use Toxic to Badly Poison a foe, and then use Leech Seed on them, Leech Seed's damage will also increment: thus, you regain 1/16, then 1/8, then 3/16, then 1/4, and so on, of your HP. Toxic will also be taking effect in this time, dealing the same amount of damage. In other words, you not only regain tons of HP, but also double the damage of Toxic, from one point of view.
To get onto the Cycling Road without needing a Bicycle, simply hold Left while the guard warns you that you must have the Bicycle to enter Cycling Road. (If you already obtained the Bicycle, this still works if the Bicycle is in the PC.) In doing so, you will bypass the guard; if you continue onto Cycling Road, you'll still ride a bike.
1. Go to route 1. Put the pokémon you want to turn into mew on the first spot in your team.2. Go to your item bag. Go to the thirdteenth item. Press select, b, b. Go into battle and select pokémon and press a on your first pokémon. Escape the battle.3. Return to either Pallet Town or Viridian City.4. Go back to route 1 and repeat step 2.5. Go to the daycare centre. Give him the pokémon in the first spot and take the pokémon back. Your pokémon just became a mew! It still has the name of the pokémon it initially was so I'd like to go to Lavender Town where the name rater can change the name of your pokémon into mew.
In the Japanese releases of Pokemon Red, Blue, Green, and Yellow, as well as all versions of Pokemon Gold, Silver, and Crystal, there is a glitch involving Substitute - no matter the accuracy of the move, if it is a move that absorbs HP (e.g. Absorb, Giga Drain, Mega Drain), the move will have a 100% chance to miss!