We're not entirely sure if this isn't an early April Fools gag or not, but if it's not we're incredibly jealous of this special Sonic Advance/Sonic Adventure 2 Battle download being offered at Japan's GameJam2 festival, where Sonic Team is providing fans with a special Knuckles Chao!
Attendees to the game festival can download the data for this limited edition themed critter from certain kiosks, assumedly to their GBA copies of Sonic Advance. From there, you can take your handheld home and import the Fighting Freak Chao straight into your Gamecube's Sonic Adventure 2 Battle via the Chao Garden.
If you don't have a copy of Sonic Advance, but you have a GBA and want to take Knuckles Chao home with you, these download kiosks will also download a temporary version of Tiny Chao Garden with the Knuckles Chao onto your GBA's flash memory.
The GameJam2 festival is currently taking place in Tokyo's International Forum on 30th and 31st March 2002. SEGA is also offering various Sonic Team-themed gifts for attendees as well, including a Sonic and AiAi (Super Monkey Ball) themed tote bag and PuyoPuyo... ball... things.
Source: Sonic Team