Engineering (XCOM2)

Engineering and item purchases work a little different with young Miss Shen: main armor and weapons/subweapons only need to be purchased once to 'unlock' them (hence larger down payments of resources), upon which you have an unlimited supply that'll be auto-applied to all soldiers (in terms of internal logic, assume she made 6, enough for a full squad). The Proving Ground items are bought more traditionally, with a build time and a greater variety of material costs (including Elerium Cores, which can only be found as mission rewards and as loot drops from enemies), such as the E.X.O. Suit armor, and the Spider suit, as well as item weapons like the special grenades.