The Battle of Tomakul taught Urza not to rely on fickle reinforcements.

Masters Edition IV

Obelisk of Undoing

{6}, {T}: Return target permanent you own and control to your hand.

{6}, {T}: Return target permanent you both own and control to your hand.

o6, oc
T: Return target permanent you control and own to your hand.

o6: Return any of your permanents in play to your hand; enchantments on that permanent are discarded. Can be used only on permanents you cast.