I'm going to be playing a kraken caller and I might take the giant squid as my companion. Does it only have one tentacle attack??
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Yeup, seems like it.
I'm guessing that the "tentacles" attack represents the squid's attempt to attack with all of their tentacles at once. This is better supported by the monster stat block where the tentacles attack has much larger dmg dice than its bite attack.
Turns out its only the Giant Octopus that gets multiple attacks.