Misleading Signpost

Redirecting an attacker is old technology: Redirect, Deflection, and a small family of spells have long let you point an incoming swing somewhere less convenient for its controller. The wrinkle here is that the effect is disguised as a mana rock, and the disguise runs deeper than a flash body: the reselection is an enter-the-battlefield trigger, so this only redirects if you flash it in during the declare attackers step, in that exact window. You cannot ramp with it on turn three and cash in the redirect five turns later; the artifact you leave in play is nothing but a source of one blue mana, because its one combat trick fired the moment it entered or not at all. That collapses the two modes people want it to have into a single choice made under combat pressure. Held in hand it behaves like any instant, giving nothing away until you tap out for it after attackers are declared, then reassign one attacker to a new legal target: off you, onto another player, or (the sharper line in a multiplayer pod) onto a planeswalker or battle that now has to absorb the hit. Cast it early instead and you have traded the trick for durable fixing, a permanent blue source that will never redirect anything. The design lives entirely in that timing: it wants to be a rock and a bluff both, and forces you to decide which, once, at the least comfortable moment to decide it.