Ok A few challenges have come to mind. PM me or review if you are interested.

Harry Potter and Naruto crossover:

Harry has died during a new war that popped up with in the Wizarding world 90 years later. However Death does not let the hero of the second war with Voldemort go peacefully into the afterlife. Instead Harry is reborn in the Naruto universe as one of the 9 Jinchuriki. He can be anyone of them and owe his allegiance to whatever village. He must however be paired with the reincarnation of either Tonks if a guy or Malfoy if a girl. Either way they should regain their memories of past lives.

Harry Potter and Fairy Tail Crossover:

Harry and any character of your choice are sent to Fiore before Erza joins the guild. Harry and whoever you choose to go with him must join Fairy Tail. They must also have ability type magic. Finally they must take a job that entails them bringing down the Tower of Heaven and saving the slaves. Whether Jelal is manipulated or not is up to you.

Yugioh and Bleach Crossover:

What would happen if instead of Zangetsu Ichigo's Zanpakuto spirit was the spirit of a millennium item? Here are the rules for this challenge. First Ichigo must find out about his Zanpakuto being in a dormant state before his first battle with Byakuya. Second the sealed state must become the Millennium Item once he learns it's name. Third for the Shikai use your imagination but don't get carried away. Finally the spirit should be the holder of the item i.e Yugi Moto(Millennium Puzzle), Ryou Bakura(Millennium Ring), Ishizu Ishtar (Millennium Necklace), Malik/Marik Ishtar (Millennium Rod), Maximillian Pegasus (Millennium Eye, For this one he has to give up one of his eyes), Shadi (Millennium Ank and Millennium Scale)

Yugioh and Bleach Crossover:

Instead of using the powers of a Fullbringer to regain his Shinigami powers Ichigo finds and acquires the power of a Millennium Item. This can be any Millennium Item and can also be tied into the Yugioh storyline or any of the other Yugioh series storlines. He must know how to play Duel Monsters. He must at some point become adapt at using the power of the Shadow Realm and most use Shadow Games frequently. His continued use should also make him crueler with each game but not to the point where he's evil. He will basically make a Yami for himself who is in charge well in the Shadow Realm to replace the missing part of his soul that his Hollow represented.

Yugioh and Harry Potter Crossover:

Instead of Yugi and other characters from the Yugioh series going to Hogwarts Harry and Tonks go to Japan and a special magic school there. Rules are as follows. 1) Tonks must be the same age as Harry. 2) Seto must be at the school and believe in Magic. 3) The holders of the items should be Yugi and Atem Millennium Puzzle (Magic has allowed the Yami's and Hikari's to exist at the same time), Ryou and Bakura Millennium Ring, Millennium Eye should be ownerless but eventually belong to Tonks, Millennium Rod should be won from Marik/Malik by Seto, Millennium Necklace should stay with Ishizu, Millennium Scale should be gifted by Shadi to Malik/Marik, and Millennium Key should be won from Shadi by Harry. Harry and Tonks decks are up to you as is Shadi's. Pairing should be Harry x Tonks.