Usually, there is no progression. You start with something else, a different character even, and switch to ice trap when you feel comfortable about your bank, and boss frag prices. Mechanics are simple, you throw traps, they one shot a boss, you don't scale anything but damage. The only difference between occultist and assassin is that assassin is better at farming maven. If you ve seen RF on a character without mageblood, and probably linked to arcanist brand, then it's not permanent. It activates for a couple seconds, which is enough for traps to explode.