Sangriaz's solution is correct but missing useful details to help speed things along.
note: it is useful to combine this with the ultimate achievement.
requirement: you must have the twin shot, three way, and rebound shot powerups active at same time.
how to do this:
- you want to have all 3 power ups on screen simultaneously ready to pick up.
- to get power ups to appear, you must kill spiderbots. spiderbots do not appear on every level. But you know when and where one will spawn because a tan triangle shaped arrow will appear on the edge of the board showing you the direction it will come from.
- after the power up you want appears, DO NOT COLLECT IT. It will persist between levels. I have heard others claim power ups disappear after a set number of stages. I have not seen this
- THE NERF BOMB WILL ALSO DESTROY POWER UPS. The nerf bombs are the larger flashing squares inset with a skull. These drop from destroyed nerfroids (toy robot looking enemies that leave a trail of small skull dots). If a power up gets caught in the bomb's blast radius, it will disappear. If you happen to have a bomb appear, you can try pushing it out of range by shooting it before it explodes.
- key to making this and ultimate achievements easy is abusing the hell out of Ultratron's save system. The game saves every level. If you pause and quit to main menu, you will get the option to continue when you press start. This will reset the level you were just on. If you accidentally lose a power up, this will bring it back. You can also farm power ups by restarting a stage that has a spiderbot on it. you can keep killing and restarting until it drops what you need.
power up symbols:
twin: looks like roman numeral 2 (II)
three way: looks like roman numeral 3 (III)
rebound: symbol looks like bullet bouncing off wall. resembles letter V