The Bohrok invasion also introduced some new Rahi into the story, because the designers came up with a bunch of combiners and had nothing better to do with them. This means the Rahi archetype experiences a bit of growth in this expansion.
For the Level 4 group (Remember: Special Summon themselves from the Pendulum Zone, grant effects when used as Synchro Material), there are two new additions.
The Waikiru is a creature with two sides in multiple ways: Slow on land but quick in the water, and docile at rest but aggressive when threatened. It changes much like monsters change their battle positions, so that’s the theme for this Rahi’s effects. A Synchro monster summoned with it gains a position-changing Quick Effect, and in the Pendulum Zone it grants appropriate buffs to your monsters when their battle position changes.
The Ghekula, natural enemy of the Bog Snake, is entirely built to be a counter to that exact Rahi from BCOR (which had effect damage as its gimmick), granting a Synchro Monster the ability to effectively redirect effect damage you take to your opponent. And if you don’t want to wait for your opponent to damage you, the Pendulum Effect provides a good source of damage as well.
The Level 3s with the banish/GY triggers get 3 new members.
The Infernavika is a small bird that protects itself from predators by hiding among streams of lava, and thus has a Pendulum Effect that can cause battles to take place in an environment hostile to all but FIRE monsters. The attribute theming continues with its effect when sent to the GY, which complements the Daikau, Ussal, and Kewa from BCOR by reviving a FIRE monster, and when banished, it can deftly escape to the Extra Deck while banishing the top card of your Deck in its place.
Serving as a steed to Matoran in the battle against the Bohrok swarms, the Keras helps out your small monsters with both its Pendulum Effect (aiding them in battle for an ATK boost) and its GY effect (carrying them across difficult terrain to protect against effects). The remaining effect that triggers when banished is anti-Bohrok rather than pro-Matoran, but still derives from the same idea.
Perhaps the most notable addition is the Hapaka, a Rahi used to safeguard flocks of other Rahi. Accordingly, its Pendulum Effect boosts the DEF of Rahi and prevents their destruction, but the more interesting part is the GY effect, or lack thereof. Instead, it has a Special Summoning procedure from hand or GY by “guarding” another small Rahi. And when banished, including as a result of its own summoning condition, it will return “stray” (banished) Rahi to the “herd” (GY).
Finally, there are two new Level 2 Tuners, both of them coincidentally birds.
The Pokawi disorient enemies by moving quickly in great numbers, so its effect weakens your opponent’s monsters in proportion to how many Rahi you have gathered up in the banished “zone”. Mata Nui Fishing Birds have a habit of swooping in to annoy larger predators and then escaping again, which I translated into a “swoopy” (if that makes sense) temporary banishment effect that includes an extra reward if used against large monsters.
These new cards mostly focus on fitting the available tidbits of lore on these Rahi into the established frameworks of the archetype from BCOR, so while they do introduce some new gimmicks and options, I’m pretty sure there isn’t any real change in terms of the overall playstyle. The possible exception is the Hapaka, which actually does break with the framework a bit and introduces an entirely new way to get a Level 3 Rahi on the field. But given the myriad of unpredictable deckbuilding options Rahi have in their current wonky state of design, it probably isn’t even feasible for me to conduct enough tests to confidently confirm or deny this assessment.
Anyway, the BBTS release includes not only a sample deck featuring all of the new Rahi, but also decks built entirely around the Waikiru’s and Ghekula’s respective gimmicks. They also require cards from BCOR, so be sure to use the complete version linked above rather than just the standalone BBTS expansion.