strengthens the prefixed adjective or adjectival noun

one who does the previous word's action: -ist, -er / (board games) counter for moves in shogi, go, etc.

hand / handicraft, skill, talent / one who does an action: -ist, -er / handwork

hand

brains (person providing intelligence) / brain trust

an unceremonious party, an event with no formality, a party where rank and position are disregarded

a sombrero

(informal) Short for メンタルブレイク.

break (a rest) / break (in sports) / breaking out in popularity, big break

Blake