Am I seeing this correct. I see no cost associated with having Reliquish or Magician of Dark Chaos on your sidebar. In both cases, when a certain points of characters have been koed, you can ko a figure on the field to replace it with the before mentioned figure(s). There is a cost on their dial, but my understanding is those cost only apply if you start the game with them, or they are koed by your opponent.

If I am seeing this correct, then it seems silly to me to not have them on your sidebar?

Yep, once the value is reached, you can KO a character and bring them in. But your opponents do get all those extra juicy points as well

That would be assuming your opponent gets the win against your extra 200+ points??? Considering how good Dark Magician of Chaos is, is there really a down side here?

I did play against him once already, and luckily I had a Dragon Piper on my force when I saw my opponent had him on the sideboard. And my main attacker was Sanga the thunderer.... 1 well timed mind control and a nicely place pulse wave took him down to size quickly.

Just luckily I had a nice combo going to counter him. But yeah, he would be tough to take down if you weren't prepared or had a lucky team

There is never a cost for including a character on your sideline.

much like all the other elements that add extra characters to your force (master mold, multiple man, ultron, team bases, etc.) the only real downside is that it gives your opponents more ways to score points. If you don't completely wipe out the opponent, those extra points can give them the win.