With the Freezer Mobile (フリーザーモービル), the boss for IceCap Zone Act 2, Robotnik will fly an ice machine that floats slowly back and forth and lowers a platform below it. The platform is spiked on its underside. Robotnik constantly sends out jets of
freezing air that will freeze you (and more than likely hit you) if you touch them. The pattern of ice jets is random and he sometimes shoots jets down from his machine onto the platform or sideways from the platform.
You must jump onto the platform and then hit his machine from below since it's out of jumping range from the ground, but the ice jets complicate this. Because their pattern is random, it's impossible to know that an ice jet won't come down to the platform right as you jump on it and freeze you in your tracks. Be very careful not to get cornered—that almost invariably gets you hit, but there's very little you can do about it. The only strategy you can use is to jump onto the platform at the right time and hope an ice jet won't touch you. Jump and hit Robotnik quickly and then scamper off after one hit into the open area. You can sometimes sort of predict where he may shoot his ice jets next but it's very hard, especially as he sometimes shoots two down in a row. This can be very frustrating especially if you don't have Tails with you. Just keep trying and eventually you'll master Robotnik's pattern or just get lucky. If you fight the boss as Knuckles, the platform will periodically go back up to Eggrobo then lower again, making hitting the boss trickier.
If you're playing as Sonic and Tails, they can break each other out of ice blocks before they get hurt, making this battle much easier.