No particular card is strictly cubeable to me. The closest cards to cubeable are Supply-Line Cranes (improvement on Castle Raptors), Flurry of Horns (2/3 haste creatures are nothing to scoff at, even if 2 small creatures is generally less impactful than 1 giant creature in the lategame) or Cloaked Siren (I can't tell if I like it better or worse than Crookclaw Transmuter. But 1 extra toughness is probably worth the narrow applications of the Transmuter's ability.)
There are some other noteworthy cards (Font of Return, Sigiled Skink) but they are below those three. I may have missed some cards (???).
Rise of Eagles is way too expensive.
So all in all, maybe one swap (Transmuter for Siren) and that's about it.
7 mana is a lot. Nessian Asp this card is not. There are plenty of strong 4-drops in green, and honestly Elephant Ambush might be stronger (a 5/7 is better than 2 3/3s, but Ambush is instant speed and can't be answered by only one removal spell).