on T-rex you lvl 10->11 and 11->12 Lvl to 13 only on epic ( baium, antharas, Valakas, Frintezza - epic, not on 4s) 100% for all in last hit pt, and on rift Anakazel with 20% to 1 person in pt.
anakzel in rift can level more than one crystal, ive done it and we leveled 2 crystals in one kill, dunno about more than 2 though