Getting three mana of one color is pretty hard in Limited, and isnt even guaranteed by turn 6 in most decks
+1/+1 counters won't affect the permanent unless it's a creature
Fast lands tend to be great filler lands to bolster an otherwise fetch land-centric mana base, especially for more aggressive decks
If heads, during your opponent's next turn, prevent all effects of attacks, including damage, done to Seadra
Straight out of the gate, Unrivaled Lethality doubles all damage that this card deals (and that can stack with double strike), not just combat damage, making it actually more like a 4/2 for three mana, but thanks to its next ability to easily get more counters when it deals damage to another creature which can quickly make this card a powerhouse
I used to ignore gold-bordered cards for their illegality in tournaments