Help me tweak Prince of Hell ED?

oldmanofdoom

I recently talked to my players about power gaming and how I wanted them to tone it down a notch and go more towards flavor and, well, they took it surprisingly well. So well, in fact, that one of my players picked an ED which is less than useful for his character IMO. Now, I really like interesting characters, as I believe that is what a roleplaying game should be about, but I also like characters to be powerful. All the other players already picked their ED (they're lv 12, but I'd rather they plan ahead so the ED can be introduced, storywise) and they are just fine, but he decided to go Prince of Hell. Now the thing is, he's a tiefling and likes his race's past to be a prominent part of his character's life and personality (something for which the ED does a good job) but he's also a bard. Now, the ED doesn't really do much for him besides raising his CHA by 2 points and giving him darkvision. Sure, the resist fire's nice and so is the teleport (even if it IS lv 30) but the 24th level feature goes to waste and the 26th utility is just plain awful. I want him to take the ED because he likes it, but I don't want this to make him underpowered compared to the rest. He was one of the most powergame-ish of the players, and I know he'll pick it because I said to go for flavor. Do you know of any way I could tweak the ED without making it too powerful but making it a more solid choice at the same time? I was thinking to let the minions be his level so their stats go up as the PCs gain levels, and giving them resist 20 all to protect them from auras (I like auras), so my main concern is the 24th level feature. Any thoughts on this? Are there perhaps feats or items he could use to make the ED more useful instead of modifying it?

Basileus

What is this in reference to? All I can come up with is to supply him with little blue _flesh to stone_ potions to mitigate the ED.