Board Thread:Questions and Answers/@comment-180.191.118.186-20150609041646/@comment-73.48.163.25-20150609064254

Fusing monsters from questing is extremely inefficient. It takes a lot of time and way too much money for far too little unit exp.

What you want to do is go to the Imperial Capital Randall and get a Metal Key from the Summoner's Hall. You get one key per day on Monday, Tuesday, Thursday and Friday. You get a Jewel Key on Wednesdays. No keys are available on the weekends.

Once you have your key, go quest until your summoner level is about to increase. Once you're set up, go into the Vortex and choose Parade Garden. Then click the lock on the Metal Parade to use your key. Then choose the area that has the same element as the unit you want to level. In that place will be Ghost, King, God and Crystal units that award absurd amounts of exp when fused. Ghosts are the most common, while Crystals are extremely rare (and give massive exp).

Since you're asking this question in the first place, I'm going to assume you're a new player. So you might not have enough energy to run through this place more than once or twice. Normally it costs 15 energy per run, but during the 1/2 Energy Vortex Event going on right now, it'll cost you only 8 energy per run.

The place will stay open for 1 hour after you unlock it. So if you level during your runs, you'll refill all your energy and be able to do another set of runs before it closes.