yeah I couldn't imagine any situation in which prince 3 would be anything other than worthless
why would you want to become a 3/3 copy of something for 3 mana? it's just totally inefficient
if you want to copy the stats for cheap, then turning into a 3/3 nullifies that effect
if you want a cheap way to create an extra token with an effect, then being 3 mana 3/3 defeats the purpose
better to either copy the stats of the target (a la faceless manipulator), or make cheap 1/1's (like a shadowcaster or the priest card that clones your minions)
It's a potential OTK piece. The problem is, there's no deck in standard that it fits into. Highlander Priest comes close, but Valen + him is 10 mana already, so (assuming you've already gotten both combo pieces) that's only 2 + 4 + 8 = 14 damage. If you managed to have a Radiant Elemental stick to the board, then toss in a holy smite and that's 30, but...
actually if I had Prince 3 I would totally try to make this work right about now >_>
Why would you use Prince 3 in Highlander when you can use Mirage Caller and then be able to use 3 drops in your deck? ---