Only four creatures remain in this thread, and several of them are silly.
BIRCH TREE SPIRIT
FREQUENCY: Very rare
NO. APPEARING: 1
ARMOUR CLASS: 1 or 7
MOVE: 3"
HIT DICE: 5+1
% IN LAIR: 100%
TREASURE TYPE: Nil
NO. OF ATTACKS: 1
DAMAGE/ATTACK: 1 hit point
SPECIAL ATTACKS: Insanity
SPECIAL DEFENCES: Spell and weapon immunity
MAGIC RESISTANCE: Standard
INTELLIGENCE: Low
ALIGNMENT: Neutral (evil)
SIZE: M
PSIONIC ABILITY: Nil
Attack/Defence Modes: Nil/nil
LEVEL/XP VALUE: V/465+6 per hit point
A birch tree spirit appears as an amorphous white cloud, smelling slightly of new, green wood. It attacks with a pseudopod with which it attempts to touch the forehead of a victim. A successful 'to hit' roll indicates that it has done so, and the victim must save vs Spells or become insane (see DMG p83). The victim also develops a white, leafshaped mark upon his or her forehead. The insanity and the mark persist until the victim receives a remove curse spell.
While in cloud form, a birch tree spirit cannot move more than 6" away from the wooden object/tree to which it is bound. It is immune to all spells, has an Armour Class of 1 and may only be hit by silver or magical weapons. However, it may be 'turned' by a druid. The druid is treated as an equivalent level cleric, and the birch tree spirit as the equivalent of a wraith.
If turned, it will return to the object/tree to which it is bound. It is then much more vulnerable to attack. Its Armour Class drops to 7, and it may be struck by any type of weapon. Fire-based attacks do double damage, and a warp wood spell will cause 1d4 points of damage per level of the caster. It remains immune to the effects of all other spells.
Birch tree spirits are bound into the service of druids or magic users specialising in plantcraft by either a hold plant or charm plant spell. It will never have any treasure of its own, only what it has been given to watch over. Because they are always guardians, they are never encountered as wandering monsters.
Also from "Tir Nan Og", by Chris Barlow, Imagine #17, August 1984