I recently attended my first semi-big tournament(60-70+ turnout) so I'll try and give what advice I can( I placed 4th after a 2nd round loss, playing Diddy the whole time..gogo Diddy!)
I'll start with Pit. Pit will start the match with arrows. Generally, I take the first hit, jump, and throw out a banana. If you're facing an experience Pit, they will know to stop spamming arrows immediatly(atleast on most stages). If not, better for you. Try and get mid-range to Pit(taking arrows if you have to) and as soon as you see him charging another arrow, chuck it at his feet. You may get hit but he will slip, setting up tech traps and nanner traps. Other than that..whenever Pit is coming after me, I try and get out a-a-tail spin (or whatever you'd like to call it) or an angled forward tilt. Pit is also one of the few characters I'm aggresive against when he is off the stage. I try and hit him with bananas, Humps, or BAir. Either way as long as you don't miss he will need to mix up his recovery.
Pikachu next. I don't have extensive knowledge, but I'll say what I can. It's pretty much alot of mindgames. Jump at him, wait for an attack, and jump again, trying to sneak a BAir in(the point being on your second jump you jump past him). If you have to, Diddy hump your way out of there. Or, atleast at low percentages, try and trade a hit..your neutral to whatever he is using(except a charged smash..don't ever trade with that). That's the only trick I've discovered, really...only played a few Pikachus. Other than that..maybe ending one of your combos with a d-tilt to prevent him countering and giving you breathing room.
Toon Link- OUCH. This is a tough one. I can't really give any other advice than to try and always keep on his tail. Little breathing room. Even if you need to take a few beatings, just breathe down his neck. other than that, try and always have an escape route if that D-Air is coming. Though, you should try and have it so TL is never above you..other than that, once again, I'm out of ideas.
Dededeeer- Hm. I played a pretty good De and it gave me a run for my money. First, pick smaller stages. This will limit the amount of time he can chain grab you(if you paly your techs correctly) If your facing a De who grabs alot(which most will) try and do one of two things with your bananas- Either set/throw them infront of Dede and immediatly charge. Hopefully he will instinctively go for a grab, causing him to slip. If not, he will try and grab the banana. PUNISH HIM. This creates a hug tilt/BAir chain possibility..just watch for him trying to get rid of the banana asap and be ready to catch. Other than that, jumping above the stars on his revory and DAir or BAir seemed to work for me.
I can't really help you on Lucario. I've only played one. Sorry.
Ike- This can go either way very quickly. With Ike's NAir. Almost any failed attack is punishment for you. The best I can say is ban Lylat, get two bananas out asap, and try and botch his recovery. Other than that, hold that shield a second longer than you think you should, try and keep a banana infront of you, and watch out for his dash-UTilt and Dash-Jab..if you're lucky you can shield 2nd or 3rd hit of jab and do a quick NAir or Fair. Oh, and at low percentages and depending on your opponents DI, DThrow to Bair-Bair works wonders for me.
ROB- Only a bit of experience. Try and choose a larger stage; the Rob will feel safer here. As with Pit, take a few hits to get Bananas out if you have to. Watch out for the Dair. To avoid it I'd say short hop in with a Bananna, drop it, and Fair or Bair, depending on their DI. Other than that I can honestly say I didn't have much trouble with the Rob I faced.
Hope this helps someone in someway; point out any suggestions/flaws in my tactics.