Pardon the Nerco and double post.
Land Wyrm and Graviton Captain are in the Creature Forge. Ghorapines is also in the Creature Forge sporting a modification of Ambush.
How can they be fine tuned?
Graviton Captain looks balanced (at least within + or - 1 range), since it has less initial damage and is slower than FFQ for greater damage in the long run. It could get a -1 cost, but otherwise it seems thematically solid.
Land Wyrm also seems balanced. I don't think it needs fine tuning.
I feel they're okay as they currently are - it seems that they both pair Ambush with other simple (but notable) concepts (Swarming and Burrow respectively), while most of the other cards seemed more situational (Lieutenant, Alligator), lacked a notable concept (Birds, Alligator), or were good ideas but ignored (Striker, Decoy).
While not actually part of the series, Ghorapines is also somewhat simple and introduces more Swarm strategies than Ambush cards, since Ghorapines isn't limited to other creatures.
Just my 2
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I get the feeling that this series is complete (at least for the 1st version of Ambush), but if others want to discuss more opportunities w/Ambush it couldn't hurt. Bloodlust and similar mechanics could also be refined and developed here.