Hmm, I forgot femaile shishi's bite deals extra damage to both undeads and demons
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I agree mind hunt may be the best way to deal with a shishi. But I think anti-thug thugs can be effective too. Considering its low damage output per hit(20, or 23 with gridle of might) and 16 MR, anyone with decent armor and a eye shield can blind it at turn 1 or 2, or you can just kill it with a troll king wielding moon blade. Shishis can neither fly nor cast returning as golems so it's not so hard to catch them.
@llamabeast: Unfortunately I omited the 2-headed forms yesterday and it seems the #firstshape bug applies to #2959 too. Anyway I have checked all Zmeys' code again and I'm pretty sure there is no other bug within it...