I dont play jiggs, but I do play ICs alot (not my main though), so I think I can give you some helpful, general advice with what to look for vs ICs.
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If you ever start a match right next to or right under the ics, do NOT start by going to them.
i.e.
on FD, if they're player 1, and you're player 3 (i think it's 3), do NOT go to them. Most IC players will probably desynch blizzard hoping you'll start by running in, leading to an early grab, leading to an early wobble, and leading to their early lead.
Same goes for any 3 platform stage where you they start to a side (Kirby 64, Battlefield, etc).
Just, when you start, dont run at them.
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Speaking of desynchs, just some general stuff to watch out for.
If you see the ICs
-dodge
-roll
-empty grab
-DD
-SHFF (no attack, just shff)
-Pivot
watch for a desynch. (Those are the main desynch setups).
More specifically, if they're far away and you're showing no notation of running, watch for Ice Blocks (which might lead to Ice Block Chaser)
and if you're sticking em pretty hard, watch for a roll-blizzard.
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Although ICs obviously dont float, i think their b.air is as long or longer than jiggs, so watch out for that. It comes out pretty quick (kinda like jiggs b.air), and it's probably one of their more frequent moves since they'll keep their backs to you for fast d.smashes.
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If you ever split them apart, you obviously want to keep racking on damage, but make sure to keep your eye out for the player if you attack the CPU ic. More often then not, if you go for their 2ndary IC, the player will either lurk over you and wait for a free hit (or a grab, if applicable), or they'll rush in headstrong to save the 2ndary IC (which is generally worse for them).
Just be sure to mix up your strategies for keeping them apart. It's not specifically hard, but it goes a long way.
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