Even `12345678` packs a punch. [Context: https://cdn.discordapp.com/attachments/852275334400835645/1059581309791518781/image0-5.jpg]

password.rb

# frozen_string_literal: true

# Assuming `PascalCase` only. Also possible: `English Case`, `Snake_Case`, …
DIGITS_CASES = %w[
  zero
  one
  two
  three
  four
  five
  six
  seven
  eight
  nine
].map.with_index {|word, i| [
  i.to_s,
  word,
  word.upcase,
  word.capitalize
] }

def number_cases(*nums)
  return [] if nums.empty?
  first, *rest = nums.map {|num| DIGITS_CASES[num] }
  first.zip(*rest)
end

def cons_combinations(*objects)
  combos = (1...objects.size).flat_map do|idx|
    cons_combinations(*objects[idx..]).map { [objects[...idx], *_1] }
  end
  combos << [objects]
  combos
end

# Search Space complexity: 4×5ⁿ⁻¹ = ⅘(5ⁿ) ∈ Θ(5ⁿ)
# Each additional digit make 5 variants:
# numeral, lower, upper, screaming,
# and (except for the units digit) repeat modifier
def iterate(number)
  number = number.to_s
  raise 'empty number' if number.empty?
  return to_enum(__callee__ || :iterate, number) { 5**number.size.pred * 4 } unless block_given?
  
  cons_combinations(*number.each_char.map(&:to_i)).each do|nums|
    first, *rest = nums.map do|f, *num|
      if num.empty?
        # solo group, use for non-repeats
        number_cases(f)
      else
        number_cases(*num).map { _1 * f }
      end
    end
    first.product(*rest) { yield _1.join }
  end
  
  number
end

(2.0**-12).then {|r| iterate('12345678') { puts _1 if rand <= r } }
binding.irb

password.rbs

DIGITS_CASES: Array[Array[String]]

class Object
  def number_cases: (*int nums) -> Array[Array[String]]
  def cons_combinations: [E] (*E objects) -> Array[Array[E]]
  
  def iterate:
    (_ToS number) { (String) -> void } -> String
  | (_ToS number) -> Enumerator[String, String]
end