This was the last gold star I needed for Standard Mode (besides completing the bonus challenges). Let's get down to the details:
This is one of the levels in the caves before the end of the game. Soon after recruiting the Dragon class, there is a level where you kill Sheep. The Extreme Challenge on this level has two paths to deal with: Red and Blue. The Red Path spawns one sheep: The Super Sheep while the Blue Path will constantly spawn basic sheep. Your goal is to kill the Super Sheep. Killing it ends the level and results in your victory.
This challenge is not going to be easy. I eventually got it, but I had to rethink some of the strategies I had been using up to that point. Keep in mind that this is part of a Hero Mode run for me and I was limited to only 6 towers (1 of each type).
I constantly was summoning and recalling my towers. I set up my ranger further into the rocks in order for her to have the most time to fire before having to move her. I constantly would move my Knight and Berserker a couple squares at a time so they could be in range. The Dragon would be a little back into the rocks just enough to have her fire breath ranged attack be able to cover all the movement path of the Super Sheep. For the Priest and Ice Mage, I had one that also tracked along the Super Sheep's path, while the other handled the Blue Path enemies. One fully upgraded unit here can easily handle them all.
I had originally tried using Lightning and the Fire Breath Magic Spells, but it could just never deal enough damage by the time it made its way around the level. The constant summon and recall was the only way I could do it. My units were around Level 50, but part of that is my own inefficiency in not realizing how much more important that is.
- Changing the speed is your friend. Pause the level completely or go down to minimum speeds while doing your recall and resummon. No penalty for doing so and it will make your life a lot less hectic.
- There is a staff in New Game + Mode that deals 3x damage to sheep. Whichever of the Priest/Ice Mage you don't put on minion duty should have that weapon equipped attacking the Super Sheep. You will need to complete some of New Game + to earn the skull currency required for the purchase.
- When picking between the Ice and Priest, consider that the Dragon's and Ice Mage's skills cancel (unless you have the Librarian book that allows both freeze and burn). If you don't have the book, then I'd recommend having the Priest as part of the moving party with the Ice Mage handling the minions. Go the opposite if you do have that book equipped (I did not have it and actually didn't take this advice, but it still worked out).
Just to give an idea for timing/distance, the Super Sheep was about 3/4 of the way around the level when I took it out. It requires constant attention keeping your units there within attack range. You can use some spells for a little extra damage, but the bulk will come from your units.