01: To the world of heroes:

Skills Rimuru cannot use:

Copy and pasted from Chapter Four:

Any skills relating to Holy magic:
Holy demon reversal
Holy demonic attack resistance
Holy demon reversal
Holy cannon
Holy bell
Holy field
Holy ray
Holy attack resistance
Secret of faith and grace

Next: Any skills relating to Dragon magic:
True dragon release
True dragon nucleation
Dragon spirit haki
Veldora
Storm dragon summoning
Storm dragon restoration
Storm magic
Velgrynd
Scorch dragon summon
Scorch dragon restoration

Next: Any skills that are related to Nullification:
Abnormal condition nullification
Natural effects nullification
Pain nullification
Physical attack nullification
Spiritual attack nullification
Flame attack nullification
Thermal fluctuation nullification

An finally: Any skills relating to Summoning:
Daemon summoning gate
Daemon summoning magic
Summon greater daemon
Summon lesser daemon
Summon greater elemental of fire Irifit
Summon medium element space
Summon medium element fire salamander
Summon medium element wind
Summon medium element water
Summon medium element earth Beast Gnome
Summon lesser element of space
Summon lesser element of fire
Summon lesser element of wind
Summon lesser element of water
Summon lesser element of earth
Scorch dragon summon
Storm dragon summoning.

To add to that, some of your slime abilities have been lost. In your human body, you will need food, blood and sleep to survive. It will take longer to generate your body in your human body. Additionally, there will be a cooldown whenever you become a slime, or use the human body.