If MapleStory could have a crossover with a TV Show...

I think Adventure Time would be appropriate for gMS but personally, I'd go for Fairy Tail. Not just because that's one of my favorite anime out there but because it involves guilds. For the longest time, guild pq has been removed / "under construction". That was one of my favorite past times to do back in the day with my guildmates. It was also one of the few ways to gain GP to level up your guild, but as of right now you can only level up or stay online to obtain GP. Not much you can do with this, in my opinion.

So here's some ideas I have (includes an idea for Masteria because I really like the old version)... If you haven't read or seen Fairy Tail, I will be spoiling a few things below.

 Spoiler

Plot:

 Spoiler

Masteria (before the alien invasion attack) wasn't truly destroyed by the aliens. Rather, most of the continent was teleported to another dimension, Edolas. (There isn't a known way to open a portal to portal as far as we know). From Fairy Tail, we know that the (former) King used a magic weapon or whatever to absorb Magnolia and transport it to Edolas since it apparently would provide a lot of magical energy. Peace was seemingly restored to Edolas after his defeat. But to connect ties with Fairy Tail, I'd say that one of the King's loyal followers survived and tried to recreate the Anima with the help of a newly created Dark Guild. However, when this guy tries to activate it, it doesn't work that well and absorbs some of Masteria (since the Anima can absorb stuff from "other worlds)" and Maplers. As a consequence, aliens (the aliens we have now) destroy what is left of Masteria. Months pass and Maplers have no idea what truly happened to the former Masteria; they assume aliens just destroyed it. During these months, that same guy tries to improve the Anima and tries it again. It somewhat works better this time, but it opens up an interdimensional portal to Earth Land and the Maple World. The Fairy Tail guild investigates it, and Maplers are curious as to why a portal has suddenly opened up. Eventually, the two groups meet up and decide to join forces after finding out a Dark Guild wishes to use Earth Land and Masteria as magic resources.

Items:

 Spoiler

- forge-able weapons and equipment

NPCs:

 Spoiler

- Fairy Tail members (Natsu, Lucy, Gray, Erza, Happy, etc).
- new maple NPCs

Quests:

 Spoiler

- once you enter Edolas, you must be in a guild to go further. Making a guild is pretty cheap nowadays anyways.
- some might include item gathering to create suitable weapons since in Edolas, magic is very limited so skill usage will be minimal. IIRC, lidium is a power source in maple so perhaps you might be required to obtain those to use your skills.
- will mention what happened to Masteria
- interaction with Fairy Tail
- (maybe you can choose sides. Siding with the Dark Guild or with Fairy Tail).

PQs:

 Spoiler

- Fairy Tail doesn't believe your guild is strong enough as a whole so they have set up training arenas. In these PQs, you may go against other guilds or work together with your guild to finish the PQ.
- Alliance PQ maybe??
- all PQs will grant your Guild a certain amount of GP.

Pets:

 Spoiler

- Since this is Edolas, you can have an Exceed (cats like Happy and Carla)!

Not sure if a new guild ranking board would be a good idea to implement in this.