Seadramon

Guardian of the lake (Seadramon)
Seadramon is one of the few exceptions of digimon that will help the player but won't join the city.

It is needed to get to the Beetle island.

Besides that it can do even more, but let's talk about the important stuff first.

Where do I find Seadramon?:

It is located at the "bottom" part of the Dragon eye lake (one screen down and left from where Palmon was)

You can only encounter it early in the morning when the sun hasn't risen yet (purple zone) or at the evening when the sun sets (orange zone).

When can I catch it?:

Despite what posts from back in 2008ish say you only need to have found the fishing rod from Trash Mountain for it to appear.

There are some hints through out the game that are directed to Seadramon like a Tankmom in Toy city talking about the "guardian of the lake" or Shellmons newspaper mentioning it but they aren't required for it.

How can I catch it?:

Either a fishing rod or the amazing rod will be required (Attention!: don't buy the amazing rod before having the fishing rod first).

Then you can take any bait as you please, like a simple meat or digishroom.

At the right time you will see a huge shadow in the back going from left to the right.

If you miss it don't worry, it is repeating its course all evening long.

You will know where it is when you see it, as the shadow isn't dark-ish as the other fishes but rather is completely black and more than twice the size of the biggest fish around.

When you align your bait with its path, it will take it all the time (if you are too fast or slow, also don't worry just wait and it will be back soon). Then it is only about patience. Only pull when the bar is white or grades over into blue.

Do that for some minutes and you will see that it loses stamina and you can reel it in bit for bit.

As soon as the bar gets yellow just leave it be, don't risk the line to snap because it sometimes pulls very strongly.

What does it do for me?:

After you caught it you get 3 options from it.
 * "Let's be friends": This option will make Seadramon your friend and it will give you a flute to call it whenever you want to travel to Beetle island. It also asks if you want to go right now (do that and go get Kuwagamon and Kabuterimon for your gym as the island doesn't offer much else).
 * "Teach me a technique": This option grants you an tech move that a Seadramon can learn and it will disappear afterwards (so you have to fish for it again). You can repeat that step till it has no moves left for you.
 * "I want an item": This option will give you a "Waterbottle" with which you can make a rookie digivolve into Seadramon (it will disappear afterwards and you have to fish for it again).