shadow the hedgehog, amy rose, tails, knuckles the echidna, matoi, and 11 more (sonic and 7 more)

Artist's commentary

Original

【セガコラボ】「セガコラボキャラクター」たちが大集合する『セガコラボガチャ』開催✨10連ガチャを確定ステップまで引くとコラボ限定キャラクターが1枚以上必ずゲットできるよ📣!!お見逃しなく🎶

https://puyopuyoquest.sega-net.com/news/210623_87935.html

I think I identified all the characters, although I don't really know anything about Sakura Wars or Phantasy Star Online. The two characters in the lower right don't seem to have tags in Danbooru.

I don't know anything about that Ulala character, but Ringo does a nice cosplay of her in the game:
https://puyonexus.com/wiki/PPQ:Ringo_ver._Ulala/%E2%98%856
To be honest, I think Ringo looks better drawn in the normal Puyo art style than Ulala does!