I think Kayla is fine and interesting for occasionals. This is where it needs the italics rules/flavor text that I usually hate.
"Draft Weenies - 4, T, Discard all the cards in your hand...."
On the Blue stun creatures, I would be ok with the Kraken in my cube but wouldn't want a 4/5 flier for 5 with the stun ability on top of that. Some cubes would be the opposite and the Kraken would be too weak. I think the big ground creature results in a more interactive game, but only control and ramp decks would want it.