The main game itself made me struggle on a few things, but once we(me and my sister) had added Gardevoir to the team and disposed of our Jolteon(lvl 44 and still no electric attack) we managed to sweep teams easier. The only match we lost was our first attempt against Greevil, but we sorted that out easily, by ditching one of our weaker Pokemon so that we'd get Shadow Lugia in our team.
Afterwards, the Orre Colessium was a lot tougher. We used our GBA games and combined our best Pokemon. The first time against Lovrina we lost(kind of) when both sides lost all their Pokemon, except for a Wobbuffet each. Stalemate. This was sorted by teaching Sceptile safeguard and we easily won.
Snattle was far easier. Mainly because our Pokemon have the wonderful Protect ability.
Mount Battle 100 challenge, whilst not overly tricky is time consuming, and gets a bit dull during the first 60 battles, where the Pokemon can hardly scratch you, and you're simply sweeping them. Still, totally needed if we want to get those GSC starters with the elemental beams. Thus far we have Cyndaquil and Totodile. Just got to do it one more time for Chikorita and we can relax.
The Battle CDs are an interesting idea(and that battle music beat the other places music...except maybe Miror B battles). A place where you have to use your brains in battle more than just your most powerful Pokemon. My jaw dropped when some guy's Primeape swept through Sneasel, Pikachu and Snorlax team.
I then realised where I went wrong, and easily sorted it out:
(Icy Wind with Sneasel...it'll get OHKO'd, bring out Pikachu. The Icy wind will have made Primeape slower than Pika, who can then use Wish before getting OHKO'd. Snorlax's turn. Use it's most powerful move, Primeape will nearly KO it, but Pika's wish will kick in, allowing Snorlax to survive another hit and finish Primeape off. Seems obvious when you think about it.)