The food XP bonus stays around until the unit dies or the map is cleared.

Thx, then i'll have to test what's faster for me. Farming for food items and doing a food dungeon to reincarnate a unit through all classes needed for the +8 stats or just mass killing lv99 food ennemies.

I probably can't afford the mana for the first one anyway atm.

Food dungeons are faster once you've got a few dungeon generators setup and a way to pretty reliably inflict gamble. In part because the minimum level for a food dungeon enemy (once you've thrown the other 8 off the map) is 1800 (9 x 200) , which is way past the point where you break even with level 99s (I think that's ~323 from memory). It's also relatively easy to keep bootstrapping your food dungeon makers levels until you hit 556, at which point you can generate a level 9999 enemy.

The level 99 trick is best for if you don't have a reliable way to produce gamble, or you're trying to get someone to level 100 (in order to make Food dungeons), or you're out of food (you can use the food markets to generate food when they first get summoned) or you need to build up mana. Or if you messed up and didn't setup a backup food dungeon generator and levelled too high / reincarnated.

If you're in Petta mode though, you can use the training dungeons for a lot of that.

Sorry i didn't answer to that earlier. Lv99 food dungeon aren't the most optimum indeed. I used them a bit but they really aren't usefull for that long.

It is however nice enough for a quick boost before being confortable enough with generating food dungeon after food dungeon.