Conqueror's Flail

The second line is the one that earns the slot: while attached, your opponents cannot cast spells during your turn. That is a narrower lock than it first sounds (activated and triggered abilities still work the stack, so mana abilities, dredge, and death triggers all remain live), but it slams the door on the interaction that actually kills your plan: instant-speed removal, flash blockers, the counterspell on the spell that ends the game. For a deck that needs one clean window to execute, that protection outweighs the +1/+1-per-color rider stapled on top, which on a heavily multicolor board is generous but strategically secondary. The cheap equip cost is what makes the lock repeatable rather than a one-shot: at two to suit up and two to relocate, you can move it onto whatever creature is carrying the turn and keep the window open across attacks. The two halves answer entirely different questions, one about board size and one about safety, and only the first cares about how many colors you are running; the spell-lock is indifferent to your palette. The defining trait is the asymmetry. Your opponents fall silent on your turn while you keep full freedom on theirs, so this is a one-directional tax rather than a symmetric pillar that binds everyone equally. The gap between a fragile plan and a protected one often comes down to whether this is already attached when you untap.