Conspicuous Snoop

The design bet is that a tribe with enough activated abilities can turn a revealed-library engine into a shapeshifting body. The first clause (playing with the top card revealed) is old Oracle of Mul Daya territory; the second (casting Goblins from the top) borrows the top-of-deck spell access that Future Sight granted. The payoff is the third: as long as a Goblin sits on top of your library, this 2/2 grants itself every activated ability that card carries. Stack the right Goblins and the same body can tap for mana, ping for damage, tutor, or sacrifice itself, all while the enabling Goblin stays in the library and the copier stays on the battlefield. The combo lines follow from that separation: the abilities work whether the Goblin they belong to is in play or in the deck. The famous kill pairs it with Kiki-Jiki, Mirror Breaker on top of the library, at which point the body inherits Kiki-Jiki's copy ability and can make an unbounded chain of hasty tokens. The counterweight is fragility on two fronts: an easily-killed body, and an engine that only ever reads the single top card. A non-Goblin reveal shuts the whole thing down. The card cannot be cast from the top (only Goblins can), so the top slot clogs until you draw it off, and the copy clause goes quiet in the meantime. The deck is really built around controlling what sits on top, not around casting Goblins at large.