Blackwind

As noted in the description, this is not cumulative. You need to have 1500 Blue Orbs collected and unspent at any given time. The game is quite generous with Orbs, assuming you destroy everything as many things in the environment drop Blue Orbs when destroyed. You can really do this at pretty much any time, but I would suggest mid game as being the easiest - early on you will want to invest in some offensive upgrades, and by mid game you should be pretty powered up, and the remaining upgrades are more for optional attacks. By this point, it should be easy to get by with basic attacks and you can start to bank your Orbs.