Those two are the reasons for the D.M.O.C to stay in the ban list
Magical Instructor Sisti
During the End Phase of your turn, if you activated a "Spellbook" Spell Card this turn: You can banish this face-up card; add 1 Level 5 or higher LIGHT or DARK Spellcaster-Type monster and 1 "Spellbook" Spell Card from your Deck to your hand. The effect of "Magical Instructor Sisti" can only be activated once per turn.
and that comes this
Magical Summoner Temper
During the Main Phase, if you activated a "Spellbook" Spell Card this turn: You can Tribute this card; Special Summon 1 Level 5 or higher LIGHT or DARK Spellcaster-Type monster from your Deck. You cannot Special Summon other Level 5 or higher monsters the turn you activate this effect.
Magical Instructor Sisti
During the End Phase of your turn, if you activated a "Spellbook" Spell Card this turn: You can banish this face-up card; add 1 Level 5 or higher LIGHT or DARK Spellcaster-Type monster and 1 "Spellbook" Spell Card from your Deck to your hand. The effect of "Magical Instructor Sisti" can only be activated once per turn.
and that comes this
Magical Summoner Temper
During the Main Phase, if you activated a "Spellbook" Spell Card this turn: You can Tribute this card; Special Summon 1 Level 5 or higher LIGHT or DARK Spellcaster-Type monster from your Deck. You cannot Special Summon other Level 5 or higher monsters the turn you activate this effect.