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Yes, you can counter a triggered ability with specific cards that say counter target triggered ability. Regular counterspells like Counterspell only work on spells, not abilities already on the stack

Like most Pokmon cards, the value of Sharpedo depends on a few consistent factors: its rarity, the printing and finish (regular or foil), its physical condition, and the set it was printed in (Secret Wonders)

In the case where Fealty to the Realm is enchanting a creature but there is no monarch, the second ability will create a control-changing effect with the timestamp mentioned above, but that effect won't do anything until a player becomes the monarch

These are all fine cards on their own