Random apply 1 of the three effects you've mentioned seems good to me..
As for effects on aliens (and other enemies) I think all enemy types should be defined with resistances, vulnerabilities & other strange reactions to various attack/damage types (like EMP might have a 5% chance to outright KO a robot but an electric attack might have a 5% chance to buff it, enrage it, make it malfunction or switch allegiance for a turn, etc)