Compared to those it is decent but now Fencer base cost the same, has more diagonal movement and armor.

I did not compare it to minions because they do not compete for the campion slot, it is bad when compared to Fencer moveset, maybe on its own is not a bad 4 cost champion but I can't think of a deck that would prefer Siren over Fencer (maybe compel is better than I think and I am mistaken, but from my experience compel is not worth more than 2 more diagonal movement and armor)