It seems he’s been turned into something of a dumping ground for more generic Dragon cards that his brother doesn’t use.
Mokuba Starter Deck:
1 Blue-Eyes White Dragon
1 Rude Kaiser
3 Niwatori
3 Fairy Dragon
3 Lesser Dragon
3 Wicked Dragon with the Ersatz Head
3 One-Eyed Shield Dragon
3 Blue-Eyed Silver Zombie
Level-Up Rewards:
Level 3: Rude Kaiser
Level 4: Monster Change: Evolution (Skill)
Level 7: Draconnection
Level 10: Dragunity Tribus
Level 11: Dragoncarnation
Level 13: Heavy Starter (Skill)
Level 14: Draconnection
Level 16: Ruins of the Divine Dragon Lords
Level 18: Dragoncarnation
Level 20: Draw Sense: LIGHT (Skill)
Level 21: Draconnection
Level 23: Ancient Rules
Level 25: Lady of D.
Level 33: Dragonic Guard
Level 35: Ancient Rules
Level 38: Lady of D.
Level 40: Guardian of Felgrand
In addition to his previously reported skills, Mokuba has two new Skills from Drops:
KaibaCorp Bling
Can be used each time your Life Points decrease by 1800. In the Draw Phase, instead of doing a normal draw, draw a random Prismatic or Glossy Card.
Monster Change: Degeneration
Can be used each time your Life Points decrease by 1500. Once per turn, send 1 Monster on your side of the field (except a Token) {to the Graveyard} to summon 1 random Monster (that can be Normal Summoned) from your deck whose attribute and type are same to and level is 1 lower than the tributed monster.