  We consider an {\em enforce operator} on impartial rulesets similar to the
Muller Twist and the comply/constrain operator of Smith and St\u anic\u a,
2002. Applied to the rulesets $A$ and $B$, on each turn the opponent enforces
one of the rulesets and the current player complies, by playing a move in that
ruleset. If the outcome table of the enforce variation of $A$ and $B$ is the
same as the outcome table of $A$, then we say that $A$ dominates $B$. We find
necessary and sufficient conditions for this relation. Additionally, we define
a {\em selective operator} and explore a distributive-lattice-like structure
within applicable rulesets. Lastly, we define the nim-value of rulesets under
the enforce operator and establish well-known properties for impartial games.
