You need to clear two Bingo Sheets to get Mokuba.
From Left to Right, the First Bingo Sheet is
Play 15 Duel(s) (30 Gems) Obtain a Card from the Card Trade 3 time(s). (20000 Gold) Open 5 Card Packs. (40 Gems) Use Spell Cards 5 times. (50 R Jewels) Unlock Joey Wheeler (Skill: Fields of the Warrior) Reach Stage 10 (DM) (40 Gems) Open the Deck Editor (10000 Gold) Beat "Mai Valentine" Once In Duel World (2 SR Jewels) Summon 20 Monsters (40 Gems)
1 Line: 1 Shield Spear
2 Lines: 50 Gems
3 Lines: 50 Gems
4 Lines: 1 Lucky Iron Axe
5 Lines: 50 Gems
6 Lines: 1 Metalmorph
7 Lines: 50 Gems
8 Lines: 50 Gems
Sheet Complete: 1 Enemy Controller
Mokuba's Skills:
Level 4:
Monster Change: Evolution
Can be used each time your Life Points decrease by 1500. Once per turn, send 1 Monster on your side of the field to the Graveyard (except a Token) to summon 1 random Monster from your deck whose attribute and type are same to and level is 1 higher than the tributed monster.
Level 13:
Heavy Starter
If your Deck has 3 or more Level 5 or higher monsters with different names, you will have improved chance of having a Level 5 or higher monster in your starting hand.
Level 20:
Draw Sense: LIGHT
Can be used each time your Life Points decrease by 1500. In the Draw Phase, instead of doing a normal draw, draw a random Light attribute monster.
From Left to Right, the First Bingo Sheet is
1 Line: 1 Shield Spear
2 Lines: 50 Gems
3 Lines: 50 Gems
4 Lines: 1 Lucky Iron Axe
5 Lines: 50 Gems
6 Lines: 1 Metalmorph
7 Lines: 50 Gems
8 Lines: 50 Gems
Sheet Complete: 1 Enemy Controller
Mokuba's Skills:
Level 4:
Monster Change: Evolution
Can be used each time your Life Points decrease by 1500. Once per turn, send 1 Monster on your side of the field to the Graveyard (except a Token) to summon 1 random Monster from your deck whose attribute and type are same to and level is 1 higher than the tributed monster.
Level 13:
Heavy Starter
If your Deck has 3 or more Level 5 or higher monsters with different names, you will have improved chance of having a Level 5 or higher monster in your starting hand.
Level 20:
Draw Sense: LIGHT
Can be used each time your Life Points decrease by 1500. In the Draw Phase, instead of doing a normal draw, draw a random Light attribute monster.