The thing with Ike is that his speed and weight class make him combo food paired with Ness' bread and butter Fair combo Dthrow into Uair or triple Fair etc. The key to the Ike match up is directly linked to how Ike approaches YOU. Ike strives in defensive play styles, like throwing out Nair and Fair, because they have large enough hit boxes to where Ike players aren't really forced to approach because approaching is a lot more riskier than putting up a wall. How do you counter this? Ness' arsenal of projectiles, notably PK Thunder, effectively forces Ike to approach. Once out of that defensive play style, now it's important to understand that Ike's strengths come from his short hop or full hop aerials, so to counter these, time your aerials in intervals where he's vulnerable either in the air or on the ground. If Ike chooses to play a more ground game, more often than not he's going to opt for tilts since they're the best option with the least amount of risk involved. PK Fire will be your best friend here since it travels far enough to outspace Ike's tilts. PK Fire is also a great move to throw out, obviously outside of Ike's tilt hitboxes, to initiate a grab combo. When opting for a grab combo, always always ALWAYS go for throwing Ike offstage since his recovery is very exploitable. A couple good scenarios might be:
BThrow at the ledge at low % - Most opponents like to jump right after a BThrow since it doesn't launch them far so it'd be good to follow up with a Bair and then PK Thunder/Dsmash depending on if they're forced to UpB or charge their Dash.
FThrow at the ledge at low % - FThrow at low percentage has a really high base knock back so if you can launch Ike offstage a decent ways away from the ledge, you can potentially steal an early kill by gimping with the tail PK Thunder. At the very least you should be tacking on some free percent.
BThrow/Fthrow from 50% to 100%~ : Assuming you don't kill Ike immediately with that BThrow, gimping is always the safest and most reward option, since his UpB is almost totally vertical, meaning he barely move from left to right. So if you strand him far off the stage without having charged his Dash, it should be a kill.
In essence, recklessly playing offense is exactly what Ike wants you to do. So you have to force HIM to play offensively so you can exploit his weight and slow moves if you time your own attacks correctly. At the end of the day, you should be trying to avoid giving Ike high percentages because he benefits a lot from rage since he doesn't die as easily due to his weight and his attack are very strong. End stocks with Bthrows or gimps off stage, or if it really gets to be higher percentages, a well spaced Bair or an Uair timed at the right moment can be the finishers.
Hope this helped
