The Special Duel Link Reg. has begun, and with it, additional missions have been introduced to farm some gems:

The missions are:
Win a Duel in Special Duels (10 times): 250 gems total
Activate a Spell/Trap Card in Special Duels (30 times): 150 gems total
Link Summon a monster in Special Duels (50 times): 250 gems total
Duel in Special Duels (3o times): 400 gems total

This results in a total of 1050 extra gems.