Prized Unicorn

The whole card is one compulsion: every creature that can legally block it, must. The body is almost beside the point, because this Unicorn was never built to win a fight. It was built to force one. It is the old Lure effect on a creature rather than an aura, and that distinction relocates the risk: kill the Unicorn and the compulsion vanishes with it, where Lure stapled to one of your real attackers keeps dragging the defending line into combat as long as that creature stays on the battlefield. That fragility is also the design's discipline. A four-mana 2/2 that pulls an entire wall of blockers into one fight is a fine deal only if you have the trample or the mass-removal payoff waiting; sent in alone, it trades for a single defender and dies. The interesting tension is the word "able." A creature that cannot legally block the Unicorn (wrong evasion, tapped, a restriction of its own) is exempt, so the compulsion reads more like a riddle than a guarantee: the attacker decides who is forced to the front by deciding what those defenders are allowed to do. It is a build-around enabler whose entire job is to manufacture a combat math you resolve with everything else on the table, and it does nothing on a board you have not already set up to punish.