Sure the updated skill sets of each class are far stronger than their originals were, but plenty of us who remember playing back then miss the experience of playing the old maplestory with those old skills.
My Suggestion is to take a skill or two that was iconic from the old version of each class and make it unlockable through some event. Certain Explorers still have this if they were created when Ultimate Adventurers exists. The vintage skill would be buffed to match the damage of a modern skill, meaning you can mob or boss with your old skill alongside all of your new ones.
Looking back, a lot of Explorers actually have pretty similar skill sets as their originals with just revamped effects and looks, so I think it might be better to have the adventurers be able to choose from a cygnus skill as well as one picked from their own job.
A few examples of skills I'd like to get back are:
Cygnus knights get the abilities their ultimate adventurers got
Corsair would get their Battleship and the 2 attacking abilities that go with it
Dark knight could get Dragon Roar
Battle mage could get the reapers that spawned on kill
Hero and paladin get buffed monster magnet? maybe it stays active for a certain amount of time and has a CD? (or just stick with cygnus's soul driver)
These skills would look like their originals, but most would be buffed to be used alongside normal mobbing skills in terms of range (how far they hit), mobs hit, latency, damage, and hit count. They could even be tied to another skill so they could get the same bonuses as that when it comes to hyperskill and 5th job nodestone boosts.
This would essentially give each class the ability to mob with a vintage skill just as well as their current skills.
