Slayer's Cleaver

The "must be blocked by an Eldrazi if able" clause is a flavor gag turned into a combat rule: strap this onto an attacker and any opposing Eldrazi is compelled to step in front of it. Lure-style forced-block effects have bent combat math since Lure itself, but tethering the compulsion to a single creature type rather than "all creatures able to block" is exactly what makes it safe to print. A wide-open version of this clause would warp combat everywhere; narrowing it to one tribe trades universality for a spike against the specific board state it was drawn to punish. That spike is a tax, not a trade. Eldrazi are famously enormous, so forcing one to block rarely means the equipped creature survives; the +3/+1 helps, but you are usually spending your attacker to drag a much larger threat down, or forcing a chump that spends the defender's tempo and dents their board. The steering is worth more than the stats. Away from an Eldrazi-heavy table the compulsion is inert text, and the card reverts to a plain +3/+1 saddled with a four-mana equip cost. That is the deliberate shape of it: excellent against one tribe, unremarkable against everything else. The restriction is not a drawback on the effect; it is the whole reason the effect could exist at all.