The Sentry is a Monster found on the first act of the Spire with two companion Sentries as an Elite encounter, and found on the second act in a normal encounter with a Spheric Guardian. Its moderate damage and aggressive Status-flooding make them dangerous in a group of 3 on the first level.
When encountered in three as an Elite, 1st and 3rd sentries will always start with Bolt while the 2nd sentry will always start with Beam. Afterwards, all sentries will keep alternating between their two moves.
When encountered with the Spheric Guardian, always starts with Bolt and then alternates between its two moves every turn afterwards.