Honestly the easiest way to gimp Ike is to get to him before he even gets a chance to up B. If you knock Ike into the corner of the screen, you want to jump off the stage and fall with him while he's recovering, just a bit below him. What you're trying to do is to bait an air dodge, and then punish it with double jump Uair (not tipman). So basically, you knock Ike offstage, he's falling back to the stage, and you jump off the stage and fall with him, out of range of his Fair but in range for your double jump Uair to hit. Ike pretty much has to air dodge in this situation because his aerials are too slow to clear his recovery space effectively, and he doesn't want to get hit by your Uair or it will kill him.
You may have to dip pretty low to bait his air dodge, but luckily there's a fairly large opening where if Ike air dodges, he'll kill himself, but if he Up B's, he won't make it back to the stage. If he hasn't air dodged before this point, then this is where you DJ Uair him, and he HAS to take it. Then he usually dies afterwards.
If Ike is recovering with Side B, just jump off the stage and throw yourself in his way. If he hits you, then he loses momentum and dies. You take a hit but so what, Ike's dead. And if you're pro like me, you can predict when he's going to let go of his side B and then you air dodge, so that the mechanics of his side B make him swing at you even though you're air dodging. No damage AND dead Ike... not sure what else you can ask for.
If you fail at baiting his air dodge, and he doesn't use side B to recover, all you need to do is get to the ledge before he does. Then use the carry over invincibility frames to Uair Ike as he's rising, as this is where he has no super armor. It shouldn't matter if he recovers low, since drop off Uair will hit him anyways.
If he up B's early/high, just drop off and regrab. If he's going for the ledge, your invincibility frames will make him die. If he's going to land onstage, just get up or getup roll (depending on timing so that you don't get hit by UpB onstage), then knock him back offstage during his up B landing lag. Also getup attack works really well if he's close enough to the ledge that he'll get knocked offstage by it. Then rinse and repeat.
If he up B's low/late while you're on the ledge, screw the invincibility frames... just go after him with tipman before he gets a chance to up B. Drop off Bair also works really well because it comes out a lot faster than tipman, and he's going to try to make you hit his super armor frames as early as possible. He'll expect the tipman but get hit early by Bair instead. If he gets hit by either of these moves then he's probably dead. Also keep in mind that if he recovers low, he has a LOT less frames to snap to the ledge, since he's only near the ledge at the apex of his up B. So it is much easier to edgehog him in this situation.
While I'm at it, general tips against Ike... dash attack and wizkick are both marvelous in this matchup, use them a LOT to punish bad spacing... much like how you would against Marth, except it's a lot easier.
Ike's jabs were really really good for a few years... now all of the cool kids just smash DI out of them. Learn how to do this and Ike's jabs really aren't a problem anymore. Good Ikes replace options that other characters would normally do (such as shield, spot dodge, rolling) with jabs, because the jabs are actually safer due to the fact that his opponent has to be shielding or he'll get hit. If you shield Ike's jabs, just roll away from him and reset, Ganon can't punish Ike's jabs unless Ike finishes the jab combo with bad spacing. And if you get hit by Ike's jabs, then just smash DI out and you'll take like 7-10 damage overall. Not a big deal.
What else..... oh yeah, Ganon's stomp is Ike's jabbing fist's worst nightmare. When Ike replaces options with Jab, he's not ACTUALLY invincible, as compared to rolling, shielding, or spot dodging. So learn when Ike is going to jab as a defensive option, then just stomp his fkin fists. Stomp > jab every time, and Ike doesn't like getting stomped because that means he has to land, which he's not great at, especially against Ganondorf.
One more thing... Ike's dash attack comes out deceptively fast, so just... learn when it hits and don't get hit by it.
Ike used to be my least favorite matchup, now he's one of my favorites. You just gotta learn how to deal with his jab, and Ganon has better tools for this task than a lot of characters do, believe it or not. Learning how to edgeguard Ike doesn't hurt either.