Elektronika in the Soviet Union created a series of handheld games in the 80s (Электроника ИМ) similar to the Nintendo's Game & Watch. How were the electronics in these games designed, especially Электроника ИМ 19 Биатлон/biathalon which is not a 100% clone of Nintendo? Given the hardcoded nature of the original Nintendo games, how would the cloned copies add different functionality?
Given that the clock part in the Электроника ИМ series, according to the wiki page, was not modified to support the customary in the USSR 24-hour mode, it is likely that there was no electronic design whatsoever, and the only thing that was designed anew were the new game scenarios and the new LCD panels that could be supported by the existing underlying game mechanisms.
Small differences in the displayed picture could be handled by a few additional discrete logic elements. For example, the target in the Biathlon game corresponds to the last (lowest) position of an egg, but when it is displayed, the figure of a biathlonist should not disappear. Therefore the signal to display it would be a logical OR of the signal "egg in the lowest position" and the signal "egg in the next to lowest position".