Repetitive flash is ridiculous, and would completely ruin any limited format in which it was printed. You could put it third from the top to be more fair.
Last resort could be printed, but probably shouldn't be given the power level of similar cards.
Artificial Knight is too good to see print, although I don't know if it would see much constructed play.
The low power level on that blue one is a bit jarring. How about
Mark of Esperness U
Wnchantment-Aura (C)
Enchant creature
Enchanted creature has hexproof.
As long as enchanted creature is white or black, it is indestructible.
Form would be abused by only having one creature of cmc 3 in your deck, making it too good.
The disciples feel a bit weak. Perhaps the red one could lose the not attack part and the white one could lose the not block part.
Others are cool and fine color-pie wise.
Last resort could be printed, but probably shouldn't be given the power level of similar cards.
Artificial Knight is too good to see print, although I don't know if it would see much constructed play.
Conceptually speaking, these are all pretty nice.
If we really want a repeatable effect, I think T is probably safest without being ridiculous.
Mark of Esperness U
Wnchantment-Aura (C)
Enchant creature
Enchanted creature has hexproof.
As long as enchanted creature is white or black, it is indestructible.