Not all spells in the game can be obtained by the player through research. These spells are those that have their specialization/class listed as Secret.
Some of them can be rewards after clearing certain exploration sites (Wizard Towers, Forbidden Sanctums, etc.) or completing the Sage Empire Quest. Others are Battlefield Enchantments that are active when attacking some visit sites, exploration sites or hexes protected by Spelljammers. For example, Arachnid Horde is always active upon entering combat at the Shrine of the Queen of the Spiders.
It is entirely possible that some of these spells are inaccessible or highly unlikely to be found, like the case of Wild Magic.
Summons a random Baby Spider at the start of each combat round to assist the caster in the fight for 7 . The spell will only spawn units as long as its owner has at least one unit on the battlefield that is not a Combat Summon.
Sustains the ritual of flames, burning everything in honor of the fire god. Immolates a random unit each combat round. Incurs a happiness penalty and damages when cast in a city battle.
Gigantic hailstones fall from the sky, causing massive destruction wherever they land. Each combat round, all units in a 2 hex radius around a random hex receive 20 and 5 damage.
The mana currents fuse themselves with supernatural beings, replenishing those creatures' . Restores 15 to a friendly Summoned unit or unit of Magical Origin each combat round.
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Cost:
This Spell is exclusive to the Golden Realms Expansion
Combat Summon.
and 8 
damage to target unit.
is restored to friendly units in a 2 hex radius around target random unit. Also dispels all 
buffs and debuffs on those units.
when cast in a city battle.
Life Steal.
Resurrects a random unit each combat round. Does affect Combat Summons also, but units which corpses get destroyed cannot be reawakened.
Ghoul.
and 4 
