They are large black amalgamations of Shadow Bugs with two jointed heads and long, two-ended blades on either arm. They lack any facial feature, except for very small bright eyes - although their appearence roughly reminds two slim, conjoined twins.
Their body has a peculiar trait as well: a sort of "core" at its center, a bright red sphere resembling a jewel. This gem is probably intended to be their heart, also being their weak point.
Shaydas always levitate and never touch the ground.
In the Subspace Emissary
Like many others enemies, Shaydas are infamous for their extremely powerful and swift attacks, which are often unpredictable. They always attack while levitating, and can move around to chase the player; their moves have also a decent to wide hitbox and range, which makes them even more dangerous.
Shaydas have four main methods of attacking:
The following list shows the damage inflicted by the combo attack for every difficulty, respectively for each hit and combined (assuming all hits chain, including the final blow):
As shown by the list, this attack is one of the most damaging moves ever, being able to deal over 250% if most or all hits chain on Intense.
While Shaydas are barely scratched by most attacks, their center (a red sphere or jewel) functions as a weak point: attacks deal double damage to it under most scenarios. Some moves have a 1,6 multiplier here instead. Attacking this weak point of the best (if not only strategy) to defeat them, avoiding great damage or a KO from their swift and powerful moves.
Shaydas usually appear in caves, although they can rarely be fought on open stages.
An odd enemy with two heads. Its legs might suggest that it's a beast of some sort, but in actuality, a Shaydas is formed by swarms of Shadow Bugs. Maybe that's why recklessly attacking it will do no good--you must strike its pink core to defeat it. Just watch out for the giant blades that it brings to the party. Mind the blades, and pick your attacks wisely!