What are some fun multiplayer 3DS games? (3+ players)

My two friends just recently got 3DS' and I was wondering if you guys could help me by recommending some good multiplayer games on the system. I've already played the following:

• Monster Hunter 3 Ultimate
• Mario Kart 7
• Star Fox 64 3D
• Resident Evil: Revelations

I must be missing quite a lot of games. We're mostly interested in a game that's more on co-op rather than competition. I know Monster Hunter 3 Ultimate fits the bill but are there any more games like it? Did a search and only found the following:

• Heroes of Ruin
• The Legend of Zelda: Four Swords

Is the latter still free? And has anyone played the former? We won't mind eShop titles so feel free to recommend whatever I have missed :) Thanks in advance!

Mario Party Island Tour. I just bought it but it has download play so you only need 1 cart to play. I know its not exactly a coop game but Mario Party games are fun with friends.

Fire Emblem has local multiplayer co-op.

I guess Animal Crossing multi-player isn't really competitive, but not really cooperative either.

Those are the only two off the top of my head with local co-op.

kid icarus has multiplayer...so does luigis mansion

Luigi's Mansion 2 has local multiplayer where you can also play with people online. Steel Diver: Sub Wars has special maps and submarines designed specifically for local multiplayer as well.