Im also including player-to-player trading sites like Cardsphere.com under this bracket because they fit here more than other marketplaces like Amazon/eBay
Another perk it has over cards like Arc Trail is that is is very hard to play around having it kill two of your dorks, against the Arc Trail you can simply stagger your low toughness dorks so that you never have two in play however Dart happily waits around to get its second kill
Territorial Kavu legitimately is a frightening card in Modern, but that's mostly because the combination of fetch lands, shock lands, and Triomes consistently allows it to be a 5/5 on Turn 2
The short version is that I believe creativity is the skill to find connections between things that aren't normally connected
Elemental Bond is probably the one Id get first, because it can trigger off of tokens, has no restrictions to how often it can trigger, and gates the trigger at three rather than four
And, by the way, it was the rare in my first booster pack too