I prefer larger stages when fighting Ike that way I have some buffer of not getting Ko'd to early. Although, I guess veiwpoints differ depends on if you gimp his recovery or not. If he's charging his side B to get back jump in front of him and have him hit you. Once this happens he can no longer do anything except fall to his death. If he waits and recovers with UpB merely edgehog him before he jumps just watch out for his massive sword that goes through the stage and could get in your way.BTW, I find it easier to kill Ike on small stages, although it may seem a bit backwards.
Does anyone else find this true, or is that just me?
As for in general his jabs and other things that build up damage are things you should watch out for. Nothing is more dangerous than facing Ike than high %. Most of his KO moves can be seen a mile a way so they should be easy to dodge. He is heavier than most characters so a bthrow will won't kill at 120 but instead at 140 depending on how he DI's.
Keep your spacing and only attack to punish his lag as Ike can and will try to outspace your attacks. On platform stages watch out if you're on the platform above him as his sword will reach you their. His Utilt has more horizontal range than you might think to me it seems the hitbox extends somewhat past the tip of his sword.
Don't fight him on the ground as its death waiting to happen so instead juggle him in the air if possible. Most of his aerials have some start up lag (except for his bair) so its easy to punish.
Pillar spiking him is also I another methods Ness could use to gimp him, as if you miss you can normally catch him with your PKT2 right afterwards. Just aim yourself for the ledge and 9 times out of 10 you'll get there before he does or hit him out of his upB. Chances are he'll be trying to get back to ledge as well.
Ike does not have any longrange or projectile attacks so spam your PKTs and PKFs. Annoy him so much that he approaches you and when he tries to get you with dash attack sidestep, punish with a grab or whatever seems plausible.
Its rather easy to punish Ike as alot of his moves have lag afterwards that you can take advantage of. Thats pretty much it, Ike is rather disadvantaged here so you shouldn't face many problems here.