I've never understood why the most common ideas for buffing Slow Start are always trying to apply extra effects on the ability.
I'd just make it so that the effect does not refresh when switching out. Make it wear out after it stays on the field after 5 complete turns, but not necessarily 5 consecutive turns.
		
		
	 
I think that's gameplay bleeding into the adjustment ideas because Regigigas isn't so powerful to where it needs a hindering ability to begin with, much less one that hits it this hard. The extra effects feel like an attempt to reconcile the flavor of the idea (which I still say is overblown in importance since literally no other Legendary Pokemon displays this kind of "rust" after being summoned/awakened) while making the Pokemon appropriately powerful (weak on one front but strengthened by a different effect to even it out).
	
		
	
	
		
		
			I don't like the Ultra Beasts.
Well no, I do but hear me out.
The concept behind them? Absolutely fantastic. Alien Pokemon from a whole other dimension, so different in their biology that regular Pokeballs don't even recognise them as Pokemon? The whole lore around Ultra Wormholes and Fallers and each of their specific home dimensions in USUM? Flippin' brilliant. I love all of that.
I mean the actual creatures themselves.
There's a quote I can't find right now in which Junichi Masuda (I think) says something to the effect of "the design philosophy of the series is 'every Pokemon can be your friend, no matter how ferocious'". And I think this is one thing that has been adhered to scrupulously throughout the series as a whole. Even some of the most ferocious and outlandish designs that spring to mind for me, like Hydreigon, Crawdaunt, and Mega Tyranitar, manage to retain that aesthetic appeal that makes me like them.
But I don't get that from any of the UBs. They're all, as a whole, just so faceless and unrelatable and unsettling. Possible exceptions are Nihilego, which is one of my favourite Gen VII mons purely for its creepiness and Naganadel, which I've been using to great effect in the Battle Tree and Battle Royal of late. Guzzlord of course is great, though I wouldn't call it a favourite.
And, to be clear, I know that this feeling of distaste is very much part of the intention. It makes sense that alien Pokemon wouldn't have that same instant sense of connection regular ones do; they are designed to be unsettling and disturbing and a little bit creepy. What gets me is just how effectively I'm creeped out by them.
So, good job Game Freak at completely succeeding with the Ultra Beasts.
		
		
	 
The thing about the Ultra Beasts for me (and I can't decide if this is a good thing or not) is how they barely even feel cohesive with each other. To an extent that might be deliberate since USUM confirms they all have different home dimensions outside of the blanket of just "Ultra Space", but artistically, I probably would have to be told some of these Pokemon are supposed to be distinctly Alien compared to normal ones.
Like, Kartana, Guzzlord, Nihilego all stray decently far from the usual conventions, two of them lacking faces entirely, biology with tenuous at best real-world bases, and other quirks like Kartana's tiny design being thin and angular instead of a chunky child like a lot of rounded First-Stage/Early Gamers (Starters, Rats, Nidos, Pikachu, etc.)
On the other hand, some like Pheromosa just feel too anthropomorphized such that she's not any more out of place than semi-Humanoid Pokemon like Gardevoir, Lucario, or to a lesser extent something like Leavanny. Celesteela similarly doesn't seem that much more alien than other "object/fixture" Pokemon like Golurk, Aegislash, or even the Rotom-Appliance designs. 
I think if I had to pin it to one factor, it's the face or lack thereof incorporated into the look. Pheromosa emotes about the same as most Pokemon, Celesteela's mouth and facial structure is very "human" despite the rest of the body, Poipole still feels like it has the "cute animal" design (though Naganadel irons that out for me). Most of the others you can't really discern a spot meant to act as a face, so you're either reading from incomplete features like Stackatacka's "eye", or their behavior/body language (which due to their body shapes may not mean anything or just be normal/reflexive to them anyway). Guzzlord mostly averts this because he barely closes his mouth to change expression and the rest of his design emphasizes incomprehensible biology like a lite-Lovecraftian creature (the Blackhole mouth, arms sticking out of that and his head, the color scheme, bizarre mix of rounding and spikes)