The Lucky Egg is an extremely useful item that will cut down on the player's level grinding time significantly - it provides a 150% EXP gain bonus to the Pokémon that holds it! It is also a trophy to any player who obtains it, as it is one of the rarest hold items in generation 2. Obtaining the Lucky egg proves that the player has dedication - or at the very least, that they were incredibly lucky.
So, what makes the Lucky Egg so rare? Simply put: Chansey. Chansey is a 1% encounter on Routes 13, 14, and 15 of Kanto in the postgame of GSC. In Crystal, this 1% chance can only be raised to a measly 2.5% with a Repel trick (which will be explained later in this guide). Then, after the player encounters an average of 40 Pokémon to find just one Chansey, it only has a 2% chance of holding the Lucky Egg. Assuming the Repel trick is being used, the chances of both of these requirements happening in a row (a Chansey appearing, and it holding the Lucky Egg) are only 1/2000! That's a tiny chance. However, there are ways to make this hunt easier on the player.
To set up for the Lucky Egg hunt, you'll need a few things first. Pick up a handful of Repels of any type from any Pokémart that carries them. 10 is more than enough. Also bring any Pokémon that has Cut, and any Pokémon that has Fly.
Next, you'll want a Pokémon at exactly level 28 with the move Thief! Thief is TM46 and can only be obtained once per game while clearing the Team Rocket HQ. If you've already used yours, you have one of five options:
1. Put whatever Pokémon you taught Thief to in the back and raise a different Pokémon to level 28
2. Check any other save files you might have to see if a Thief TM is still on it
3. Check the Pokémon you gave Thief to - if it is level 28 or under, it can still be used for Lucky Egg hunting!
4. Replay Crystal or Gold/Silver to get a new Thief TM
5. Glitch or hack one into the game (outside of the scope of this guide)
Assuming you are catching a new Pokémon for this hunt and aren't just using a Pokémon you previously taught Thief to, you have quite a lot of options! While you can use any Pokémon capable of learning Thief that you like, a speedy Pokémon is best.
Dugtrio and Persian are your best options for the job. They both evolve under level 29 and have high speed stats, plus they are easily obtainable. Just pick whichever one you're willing to look at the backsprite of and hear the cry of for a long period of time!
Once you've caught your Pokémon of choice, level it to exactly level 28 and teach it Thief. Make sure that it isn't holding any item and put it in the front of your party. If you already used up your Thief TM, just put your Pokémon with Thief second in your party. With Repels and HM Pokémon in hand, you're good to go!
This is optional, but will speed up your Lucky Egg hunt significantly over time. For maximum efficiency, your text speed should be set to FAST and your battle scene should be set to OFF in the options menu. Text scrolling and animations are so fast, they seem insignificant, but unless you're very lucky, you'll be here a while. Those tiny timesaves add over time!
You may find it helpful to feed your Thief Pokémon some PP Ups to get more Thief PP to cut down on trips back to the Pokémon Center, if you already have some on hand.
I also recommend bringing plentiful Pokéballs - not for catching Chansey, but just in case you get extremely lucky and come across a shiny Pokémon. You're likely going to be seeing a lot of encounters and you never know!
Now that you're totally prepared, head to Route 14. It's to the east of Fuchsia City and requires Cut to get to the patch of grass. You might have to fight some trainers along the way there if you never defeated them during the Kanto postgame.
You'll need to place yourself in the very top-right or top-left corner so that you can hit the wall in two directions without taking a step. Once you're in place, use whatever kind of Repel you acquired earlier. Now, you can bonk against the wall, alternating sides to get Pokémon encounters without wasting Repel steps. You essentially have an infinite Repel!
By keeping your level 28 Pokémon in the front of your party, you will only encounter Pokémon of level 28 or above. This is useful, because there are some Pokémon on this route that appear at only levels under 28. By eliminating those encounters, Chansey (which is always level 28) appears more often, going from a 1% (1/100) to a 2.5% (1/40) encounter. Any time a lead Pokémon of a certain level is used with Repels to gatekeep encounters, that's called a Repel trick!
Encountering Chansey will likely take you a long time. If you're lucky, you'll only go a few encounters between your next one, but most of the time, you will see an average of 40 Pokémon before seeing another Chansey, sometimes more. Just keep at it, and eventually you'll encounter one.
Once you've encountered a Chansey, use Thief first turn. (If your Thief user is in the back, switch and then use it. Chansey uses Minimize often, so it might be kind of annoying.) Most of the time nothing will happen other than a little bit of damage, but if you hit the 2% jackpot, you'll get a Lucky Egg with the text "[POKéMON NAME] STOLE LUCKY EGG from its foe!"
Due to a coding error, Thief sometimes has a .4% chance of not working even if the opponent is holding an item. If you're paranoid, you can choose to use Thief twice in a row.
After that, you can defeat or run from the Chansey, it does not matter which. Open your party menu, and your Thief user will be holding the Lucky Egg, which you can take and put into your bag. Congratulations! You've successfully completed the hunt.
Hunting the Lucky Egg can take you anywhere from 1 Chansey to 200 of them, although the average is 50. When I personally completed the Lucky Egg hunt, I had encountered 48 Chansey and hunted for roughly 11 or 12 hours of playtime. I had to go back to Pokémon Center three times. Your mileage may vary. However, no matter how long it takes, it will happen eventually! Don't give up!
In Gold and Silver, the steps are nearly identical to those in Crystal, however on Route 14, Chansey is found at level 25 instead of level 28 which means the player can't use the optimal speedy Dugtrio or Persian. The odds for finding wild Chansey while using the Repel trick also vary per time of day. They're actually marginally better than Crystal's rates, though! 3.85% in the morning, 3.33% during the day, and a whopping 4.76% during the night. If you would prefer to hunt in Gold or Silver, just follow Crystal's steps with that in mind.