Throgan: the difficulty (if I can try to summarize the thread) is in finding cards that fit the theme with appropriate power levels and good synergy with other themes, like not even I am throwing in Serra Ascendant. For a C/U Cube or something more carefully kept under wraps you could go nuts with Tithe Drinker and other stuff that's about that strong, but most Cubes on here have a narrower range of lifegain cards that fit these conditions. For example, Extort is mana-intensive enough to not scale well past regular draft ...
For some reason I forgot about
Rhox War Monk, a very Cube-able 3c card that I like a lot.
Sprouting Thrinax also brings me great joy, and if someone could find a real Esper card to put in my Cube I would be happy
I dunno, I jammed in a couple Pridemates today and it was great fun. Soul Warden and Suture Priest also fit well, and I'm sure a big part of that is their "free" nature