Dungeon Crawl Stone Soup: Now with 50% more Sigmund

[Dr.Feelgood]

It's one of the best utility spells in the game and it costs 1 MP. Summon Butterflies is an emergency escape spell. Cast it and run to the nearest staircase. You can also use the butterflies as a barrier, while you regenerate your MP or use smite-style conjurations. It also fits perfectly in the ultimate spell list:

Spoiler

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Spells: 21 memorised, 2 levels left

a - Necromutation
b - Apportation
c - Lehudib's Crystal Spear
d - Abjuration
f - Blink
g - Extension
h - Deflect Missiles
i - Airstrike
j - Swiftness
k - Sublimation of Blood
l - Regeneration
n - Controlled Blink
o - Haste
p - Borgnjor's Revivification
q - Flight
r - Fire Storm
s - Summon Butterflies
t - Selective Amnesia

Those translucent walls have a hidden door. Press the '5' key to search for it.