What is the last weapon in onslaught 2?

Answer 1

The last weapon that is unlockable in Onslaught 2 is called the Combonly.

It's description reads: "When built in combo range fully upgraded standard turrets it can join them together into a combo firing turret."

In other words, if you place this 'weapon' near turrets that are in a combo, you will be able to choose to create a singular turret that only uses the combo.

For example, if you create a nuke combo (two blue turrets firing into a red turret) and you place the Combonly near them, when it turn red then you will be able to create a turret that only fires nukes.

Keep in mind that only the damage of each turret is needed to be maxed before you can combo them so ignore the 'fully upgraded' part of the description.