I am very conflicted about this creature, I have written and deleted quite a few responses and still havn't come to a cohesive position. For this reason I will stick to discussing powers:
Spin Kick
I do like Spin Kick, but in its current state as a standard action it is a very poor choice for the goblin. I think it might be better as a minor action:
MINOR ACTION
Spin Kick (encounter; recharges when an enemy spends a healing surge)
Attack: close burst 1 (enemies in burst); +4 vs. Reflex
Hit: 1d4+2 damage and the target is pushed 1 square
Effect: if goblin hits at least 1 target with this attack it may shift 2 squares
Enraged Frenzy
This is fine, personally I don't think it needs the rider of 2/encounter. This is a solo creature being able to do this once a round should be fine.
Flying Body Kick
This again is a good idea for a power, but as this is a solo it could maybe to with a little extra oomph.
STANDARD ACTION
Flying Body Kick * Recharge

Attack: melee 1 (one creature); +6 vs. AC
Hit: 1d6+3 damage and the target is pushed 2 squares and knocked prone
Effect: Goblin makes a Greatclub attack against a secondary target
Thorny Net
As an attack that deals no damage it is horribly under par for a solo creature, even if used with its action point. I think it might make a good Move Action attack
MOVE ACTION
Thorny Net (poison) *
Encounter
Attack: area burst 1 within 10 (all creaures in burst); +4 vs. Reflex
Hit: target is restrained (save ends)
Each Failed Saving Throw: target takes 5 poison damage
Aftereffect: Target is slowed (save ends)
Other than that as has already been pointed out as a solo the creature really needs an at will double attack (at low level this usually specifies seperate targets).
As an aside....
Previously you have stated that you don't like "Video Gamey" elements in monster design. Without getting too confrontational about it I think the little "Cut Scenes" mechanic you introduce between stages and the fact that damage does not carry over are both
very Video Gamey.
Personally I don't have a problem with that but I find it quite ironic
