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A lot of decks nowadays require an extra deck, so this card invalidates a lot of strategies
If you're going wide, you could be picking up a significant part of your deck
For that reason alone, she's lower on this "Top Elementals" list, but she's still awesome as both an include in land-based decks and as a Commander of a massive land-count list too
(Then again, if you run out of cards, you lose the game, so it'd be pretty funny if that happened as a result but we digress.) You can use cards like Professor Juniper even when you've only got a single card in your hand, effectively increasing your chances sevenfold of having a better hand to suit your situation
(In the dub, Kaiba states that he knows these weaknesses exist - the first major weakness is that they require three sacrifices to Summon them, but since they're already on the field, that weakness was eliminated