It may not be big or flashy, but Yondu's Yaka Arrow is one of the most bada** weapons in all of the MCU. During the Battle of Xandar, Yondu put the arrow to awesome use when he became surrounded by almost 20Sakaarans.
Yaka is a metal which Centaurians can manipulate through high-frequency whistling, and when things look like they're getting tough for the blue guy, he simply opens up his jacket, whistles, and the arrow makes short work of his enemies, piercing through the armour of all the Sakaarans and also bringing down a Neocraft with another soldier inside.
It figured only briefly in Guardians Of The Galaxy, with James Gunn wisely not overusing it there, but we got to see its full capabilities in the sequel to brilliant effect, most notably in the prison sequence with Rocket. It's an almost hilariously over-powered weapon which can make mincemeat out of grunt enemies in no time at all.