Sorry I was silent for a while, I got a bit consumed by the Sasquatch race I'm workin' on.
Well, it's definitely a more interesting enemy now.
I have a question about size control. Can he change all the way from diminutive one round to colossal the next, or can he only go up or down one size at a time? Also, there should probably be a clause about him being unable to grow larger than a space he's in, or include burst rules like enlarge person/animal does.
Bad omen is certainly an interesting idea. I could certainly see the haakapaizizi being used as an indirect encounter. Like, it just walks past the party in the wilds and inflicts bad omen on them before they're to go do something important. A -2 doesn't seem like that big a deal though, at the level we're talking about actually engaging the critter at.
These guys look pretty solid all around. I think the damage should be +3 on the spear, and I think the grapple mod's off, but those are the only problems I can find.
Honestly, I think that going bigger would have made them more threatening. Juvenile's alright for really low-level parties, but hatchling is just silly. A tiny-sized creature that's not just stronger than an average full-grown human, but stronger than a sizable majority of humans. tiny size is like a foot-and-a-half, max.
Then there's the swallow whole ability. At small size, it's practically useless against PCs. It could be used to eat a wizard's familiar, but that's pretty much it. And at tiny, there's pretty much no point anymore.
In the full attack section, it should be primary bite, secondary bites, and claws OR tail slap. As they're being used as a secondary attack, though, the claws in the full attack should deal half str damage.
Really cool monster!
Your formatting is missing a few / around ref and will saves.
I think the attack bonus with the spear should be +12. +7 BaB, +6 str, -1 size.
The damage bonus on the spear should be +9 if my math is right.
If expand increases them two size categories, the size bonuses and penalties are off. They would increase to gargantuan size, and their size mods would be +4 to CMB/CMD, and -4 to attack and AC.
I'm somewhat confused about the the ice heart. Can you try to clarify what exactly it is? You say only the heart of a redeemed chenoo can be used, but in redemption you mention their heart thawing, and there's a mention of a lesser ice heart shard which is just confusing to me.