TEXT: The Demon Shaman
  This sub-class of a magic-user has the ability to gate in demons, and use magic-user 
  spells at a limited level. This is the ability:
  Level
  % To Gate
  1
  5% Type I
  2
  10% Type I
  3
  20% Type I
  4
  25% Type I, 5% Type II
  5
  40% Type I, 10% Type II
  6
  45% Type I, 15% Type II
  7
  50% Type I, 25% Type II
  8
  60% Type I, 30% Type II, 5% Type III
  9
  70% Type I, 35% Type II, 10% Type III
  10
  75% Type I, 40% Type II, 20% Type III
  11
  75% Type I, 45% Type II, 25% Type III, 5% Type IV
  12
  75% Type I, 50% Type II, 30% Type III, 10% Type IV
  13
  75% Type I, 55% Type II, 35% Type III, 15% Type IV, 5% Type V
  14
  75% Type I, 60% Type II, 45% Type III, 20% Type IV, 10% Type V, 5% Type 
  VI
  To gate in a demon, first roll for the strongest type of demon, and then go down. For 
  example, a 14th level shaman must first roll for a type VI demon. If this roll is below 5, a 
  type VI demon appears, if it isn’t he must roll for a type V demon, and so on, and so on. A 
  shaman may also start on a weaker demon to reduce gating time and 
  Gating in demons is hard and tedious work, and afterwards the shaman must rest for at 
  least a day. To gate in a demon the shaman must have a skull, human or animal. Gating in 
  a demon takes a while, at least one segments per type of demon, for example a type III 
  demon takes three segments to summon. This time is rune drawing, and chanting. While 
  gating, a shaman cannot do anything else, and is in possible danger of attack. A shaman 
  must be evil.
  After gating in a demon, the shaman must keep it under control. It is checked every round. 
  There is a 10% chance per level of demon that the shaman loses control. If he does so, 
  the demon immediatly attacks the shaman and then goes into a complete frenzy. If the 
  demon stays under control, the shaman can gate him back whenever he wants. When he 
  wants the demon to leave, the demon simply dissapears. The shaman does, however, 
  have a +5% chance of loosing control in that moment, so unless the demon is killed, the 
  shaman is always in a reasonable amount of danger.
  Shamans may work together to add their chances together. This counts for control and 
  summoning chance. However, one segment gets added to the casting time per additional 
  shaman. Often, an evil rich man has multiple shamans working for him.
  A shaman has some knowledge of basic magic-user spells. For the spells that he knows, 
  use the magic-user spell table, but subtract one level of each spell except for the first one, 
  and all spells above third level are at minus one amount. So a shaman that woulld 
  normally have 3 fourth level spells only has two.
  
SOURCE: textdata/thevault/Dungeons & Dragons [multi]/1st Edition (ODD, D&D Basic, AD&D)/1st Edition/3rd Party/Dragonsfoot/Classes/Demon Shaman.pdf