Well, for example, Gremlin Leader and Reptomancer don't have hardcoded patterns but they will not do the same attack twice in a row, that's what I mean by "semi-random". A lot of enemies are like that, they cannot use the same move more than x times in a row.

Some enemies have fully hardcoded patterns, or hardcoded patterns with multiple choices like you say, like the Heart. That's maybe less "semi-random" and more "hardcoded with a bit of randomness".

(I'm not sure which is more common between the two actually, I don't pay that close attention to attack patterns of normal enemies.)