B:B is the same as B1:B1048576 and references 1048576 rows which can raise performance problems and therefore should be avoided if possible.
For example, if you control Rin and Seri, Inseparabler as well as a permanent with "Each Dog you control enters with an additional +1/+1 counter on it" and you create a 1/1 Cat token, that Cat token will be a Dog Cat token and will enter with a +1/+1 counter on it, a woof, and a purr
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You can do that with one card pretty easily and so for Exploration to be worth it you need to really take advantage of the mana or two you save and the slightly earlier ramp it can bring
I remember my first mini-score on eBay, a playset of 4x Blazing Archon for $2.71 shipped
The Pokmon TCG is continually evolving, and the developers are regularly experimenting with new ideas and mechanics