Watch Dark Cloud 2: Lure Dupe Glitch from spoonshiro on www.twitch.tv
Easy enough - just equip Max with the Lure Rod, switch the inventory page to Monica or the Ridepod, select another Lure of the same type, and put it on the rod. You'll dupe it. Repeat a bunch of times, then take them off and sell them for a boatload of cash.
(Thanks as ever to Pokemonfan4000!)
As for monster transformation... well, it's trash, but you do need it for a few Medals and a trophy, so you'll just have to deal. Your best best is honestly just to have Monica kill an enemy with her normal weapons (preferably with Abs Up bonuses), then transform and collect the points. In Moon Flower Palace you can usually gain 2-3 levels per floor.
Only one monster is required for the trophy, so I stuck to the Gemron - I can use it at a distance and stunlock enemies with on a fairly reliable basis. At three level landmarks - 26, 51 and 76 - you'll unlock a new, slightly more powerful (but still pathetic) form and gain a Monster Drop, which actually is a pretty good synthesis item.
...Not at all worth the sheer amount of grinding it takes to get just one, but it's a nice consolation prize on the road to everything else, at least.