Where you find it: There's only one way to get a hold of the Sentinel's Plasmacaster, and it isn't easy. The special piece of tech is sold by that whiny crone on the Brotherhood Of Steel's Prydwen airship, but only if you've completed the main story. Finally ridding the Commonwealth of The Institute will trigger some drastic changes in Boston, not least the replenishment of vendor inventories with more lucrative items, including this one. Why you need it: Energy weapons are arguably among the strongest in the game with the right character build, but the Sentinel's Plasmacaster is on a whole new level in comparison to its vanilla brethren. Besides the fact that plasma weapons are already borderline OP without unique perks due to their split ballistic and energy damage, the Plasmacaster also does double damage to enemies if they're at full health. Use it in V.A.T.S. while under the critical damage effect and watch it eviscerate your enemies in one fell swoop. It's not the best energy weapon though...