- Dragon Ball X Superman:
Yes i know that its clichè at this point but i still something that i still want to see happening officially, mostly to see them interacting with each other rather than having them fighting, or its not like we have to use their most current version.
If i was in charge of the project, i would have a crossover take place in an AU (an Earth which is a mix between New Earth and U7 Earth), where Kid Goku ended up bumping into a young Clark Kent, for clarification this happen during the timeskip before the Tien Shinhan Saga, which its why Kid Goku was on Smallville since he was travelling and training in preparation for the 22nd Tenkaichi Budokai.
This version of Clark will not only be aware of his alien origin already, but his classic superpowers (Super Strength, Super Speed, Invulnerability, Super Hearing, Super Vision, Heat Vision, Flying and Super Breath) would have manifest at this point of his life, although he isn't nowhere near as strong as he it as an adult.
It would really be interesting to see how they two would react to each other, due of both their similarities and their difference, like i would have Clark be a bit shy and far more frightfull to show his true nature (in fear to be rejected), Goku its instead full of joy and he don't have problem to show who he really is to other.
- Godzilla X Cthulhu Mythos:
Another crossover who was as well ton of potential, as both stories have very similar themes such as humanity's powerlessness in the grand scale and how much insignificant they are, but while Cthluhu rappresent the fear of forces beyond human understanding, Godzilla rappresent the fear of forces beyond human control.
This version of Godzilla, in my opinion, should be somewhat of a mix between Legendary Godzilla and Shin Godzilla, take the primordial force's aspect of Legendary, the nuclear/atomic horror's aspect of Shin, mix them together and you get probably Godzilla's best version possible,
so something like this.
For the story, i guess it would be like having a Cthulhu Cult trying to awoke their lord by mind control various Kaiju for their bidding, with would trigger Godzilla as this threat the balance of the planet and due of this he will directly retaliate to humanity itself, and as the main human character i would have the classic old fashion detective/scientist who decide to investigate why Godzilla its angry.
The end can be have both Godzilla and Cthulhu fighting each other other to end in a stalemate, where Cthulhu return to his eternal slumber, Godzilla too, the Cthulhu Cult get killed and the main human character ended up in an asylum (called Arkham because fanservice), where he not only become mad due of seeing Cthulhu for too much but he its also slowing dying due of radiation poisoning as he was also too close to Godzilla during the final fight.