Summary
Stand off Iggy has the smallest hitbox and the fastest walk speed out of any character in the game, which means many combos and moves will flat out not hit Iggy. You can try to bait an opponent into attacking Iggy's large stand hitbox, just to turn it off and punish accordingly. Be careful, though, many moves can still hit even if the animation doesn't look like it. He has an airdash, but it's more of a glide forward, and can only be done once per jump. His combos aren't very long or complex, but do decent damage for what they are. His grab is also excellent, a hard knockdown that lets you set up your many oki options.
Iggy heavily relies on his ability to either force his opponent into nasty guessing games or his okizeme options. In some matchups, he'll be rushing you down, in others he'll be hanging back, waiting for you to make a mistake. He needs to have a good grasp of when to switch from stand off to on (and vice versa). You'll need how to know how his sandballs work, and to apply creative pressure and reads. If you get your opponent in the corner, his pressure gets very scary. As Iggy, you'll want your opponent to get panicked and predictable. If an opponent is on very low health, his sandballs suddenly become a lot scarier. That minimal damage is gonna be a water(sand?)fall of potential death to a very low health enemy.
Iggy's IOH (Floating, throwing a sandball and landing with an aerial as early as possible) is very important to his game. You can go into your BNB or even start a corner loop from it. Many characters have trouble approaching you and your sandballs, so sometimes you've got to lay back and let the opponent run into you. If you get predictable, you will get anti aired. So be careful when using it, but dont get scared of using it.
Okizeme
You have many okizeme options as Iggy. Here is a few generic ones, feel free to experiment with these options to not get predictable. It's VERY important to note that if you hit someone on their first wakeup frames, you will not be able to combo into 63214+A/B/C due to a glitch. If your opponent does not know about this, they may stand still and get hit anyway, but it won't work on more experienced players.
s.8[8]A s.2A/grab (hold 8 for a split second)
A simple light sandball into either a low or a grab. If they block low, you can go for the grab. If they think you'll grab, they may try to tech hit but be hit by the s.2A.
A/B Sandball, j.s.B/C
Iggy's instant overhead! You mix this up with a simple low. Both lead into combos, so if you're not that confident in your meaty timing you can do this. instant overhead can be rolled out of by faster rolls, so if your opponent tends to roll when they see you take to the skies, try baiting out a roll by doing it a tiny bit earlier, so you have time for your grab.
63214+C, j.C
You jump over them with j.C and let the commandgrab hit them. This works on characters with medium to slow wakeup time. Beware, if the opponent knows how to escape (either guard cancelling or getting hit by the j.C, then jumping out) you WILL get punished. If the j.C doesn't hit meaty either you'll be in for a world of hurt.
6B OR 2B xx 236+AA/214+S
You simply make them guess if you hit high or low. Pretty simple. You'll get most of your damage from this against many characters. It all depends on the wakeup time, although this works against the majority of the cast.