Rhox Meditant

The conditional cantrip is the whole point: a 2/4 body that holds the ground fine on its own, but only replaces itself in a deck willing to pay the green tax. This is design built to sell two-color play, the kind of reward that goes to the player committing to white-green rather than splashing it. The body matters more than the rate suggests. A 2/4 for four mana blocks most early aggressive creatures cleanly and trades up against the curve, so the draw is a bonus on a creature you would sometimes run anyway. The intervening 'if' clause does the policing work: the ability checks for a green permanent the moment the Rhino enters, and if you do not already control one, the trigger never goes on the stack at all. There is no window to flash in a green permanent after the fact, because nothing is waiting on the stack to respond to. That single restriction prices the effect down from an unconditional cantrip body like Sea Gate Oracle to a domain-style payoff. It is plain design, and deliberately so: a common-rarity reward for honoring a multicolor commitment, doing its job for the player who built toward green and nothing for the player who did not.