In the third and fourth generations, which pokemon require events?

Between the third and fourth generation of Pokemon games, which Pokemon cannot be obtained without an Action Replay or similar in any of the GBA/DS games without going to a Nintendo Event?

And are there any event Pokemon that are still not attainable without an Action Replay at all?

Solution 1:

The event-only Pokemon for 3rd Gen are:

• Mew
• Lugia
• Ho-oh
• Celebi
• Deoxys

Jirachi can be acquired with the Pokemon Colosseum bonus disk (that's where mine is from ♪).

The event-only Pokemon for 4th Gen are:

• Celebi
• Deoxys
• Darkrai
• Shaymin
• Arceus.

Mew can be acquired with Pokemon Ranch, while Lugia and Ho-oh are caught in Heart Gold/Soul Silver.

Solution 2:

Currently, in HG/SS, you cannot get Spiky Eared Pichu by any means other than doing the event for it. That would be where you take the Pikachu-colored Pichu to Ilex Shrine and make friends with it.

You can hack the shiny event Pichu to get the event, but to my knowledge, there's no AR codes floating around for the Spiky-Eared Pichu specifically. It may have changed since I last checked.