Post 2/2: To stun them I used the sword Blizzard and used Unleash. I also bought alot of stunners from the shop (about 15) that Naz could use if Unleash failed. This way I kept at least 1 of them stunned almost all the time, so they could never use their Instant Death skill twice in a row. I also tried to lower both their hp equally much all the time, so they couldn't revive eachother once I killed them. After them the next problem is the Final Boss, which I think is easier. Just remember to use Barrier and Protect and Naz' special skill to keep your defences up. And you can always use Tactics-Defend which is really useful, at least in the first round because of the Ion Canon skill that the human enemy has. Good luck =)
Post 1/2: This is how I got the impossible badge: I got the Bunny!, Bunny!!! (two must haves), Thunderclap, Magic Counter, Astrology, and some other skills for Naz, and Aerial Support, Secret weapon (also two must haves), Cat Tamer, Counter, Sword heart and some other skills for Matt. To get these skills you have to use the associated attack/summon or whatever it is. For example: to get Aerial Support you have to use Air Strike alot and to get Bunny! you need to summon Slime Bunny alot. You should just focus on getting these skills all the way to the Hydra heads, which IMO is the first difficult obstacle. To get past them I focused on stunning them alot, since their Instant Death skill is a pain in the ass.
This game is extremely boring and really easy. I used an agile Wildcat and went for dehydration in the begining. When I got higher level I took Entropy Blast (Energy V) which kills almost everyone in 1 hit if you have Perception, Cordination and Instinct maxed. With Entropy Blast the game was too easy and just repetitive, I even 1-hit KO'd Waizer. 2/5
I totally agree with Leprekan so I'm going to quote him "Fairly simplistic game, gets repetitive after awhile and you'll only need about 2/3 of the upgrades to beat it. A decent game over all, 3/5"