The Hi5 Treasure Hunt Event is available when you talk to NPC Joyce. She will transfer you to an event map where you hit little green boxes in order to obtain items.
You may climb up ropes or hit boxes to enter hidden maps.
The time limit for the event is 10 minutes and is repeatable once you exit the event map. Just return to Joyce.
Scrolls that you should watch out for:
which drop (or pop-out) from the boxes as well as potions such as Elixir, White Potions and Return to Town Scrolls.
Also you will have to look out for a Hi5 Treasure map. You may only hold ONE Hi5 Treasure map at any give time.
After you have recieved the Hi5 Treasure Map, talk to the other NPC called Vikin (i think) and he’ll reward you with a random gift in exchange for the treasure map.
You might recieve various MapleSEA Anniverary cakes but who knows, if you’re lucky, you might just recieve a 5th Maple Anniversary Chair. It is however unfortunately untradable.
Hint: For a better chance at obtaining Hi5 Treasure Maps, enter hidden maps especially the ones with the mushroom houses. At the first map, climb to the 2nd portal on top. Enter and search for boxes which take you to hidden maps.
PS: Apparently there’s a bug when you want to sell things through the MTS. When you place your item for sale, you will disconnect and when you check back the MTS, your item will be gone. This however does not apply to everyone.