...wow. Lots of controversy regarding Heart Swap VS Power / Guard Swap right now. Personally, I'd like to see Heart Swap disallowed and Power/Guard Swaps allowed... I agree with DK and RD's conclusions about Heart Swap for the most part, I just arrive at a different conclusion.
Which is largely why I'm neutral about Heart Swap right now. I can demonstrate a viable set using only the mechanics involved in Power Swap. Heart Swap is basically Power Swap on steroids. Heart Swap allows you to do incredible things with Superpower and defeat things like Crocune and Curselax by taking their offensive and defensive boosts simultaneously. It's like Psyche Up combined with a single-field Haze for most practical purposes, which is why I think it needs more consideration. Power Swap is demonstrably useful and not overpowering, Heart Swap might be overpowering, but aside from being able to use Superpower + Heart Swap to obliterate any Blissey fool enough to stay in, I can't say it doesn't apply to a much larger list of threats.
The things bolded in here are why I'm so hesitant to allow Heart Swap. I do think that it would allow Kril to beat a lot of things it shouldn't be normally. I agree with the practical uses of Power Swap and I really like the set Deck Knight came up with, as it fits the concept perfectly, but if you turn the Power Swap into Heart Swap that worries me. So I say
disallow Heart Swap.
Snatch - Sort of in the same boat as moves like Magic Coat and Power Swap to me; potentially useful against certain threats, but too situational to really be truly effetive. I say
Allow. Honestly, I think this move relies way too much on prediction to even be competetively viable, kind of like pre-Shadow Tag Wobbuffet.
Encore -
Disallow. This move's sole purpose is to make room for things to set up, and that's not what we're after with this concept. This move is in the same boat as Taunt far as I'm concerned, and has no business being in Kril's movepool.
Substitute /
Rain Dance - I'm not entirely sure why these two moves are even controversial, since everything gets these anyway. Substitute can't be any more broken on Krilowatt than anything else out there that likes to abuse it, so
allow Sub, which no one should even need to point out IMO.
Rain Dance seems more potentially useful on Kril to me, and I can easily see it being used as a Rain Dance setup+abuse Poke, which is dangerously close to sweeping... However Kril still doesn't have the raw stats to truly sweep, and things like Latias that resist its STAB Surfs and Thunders are still as capable of forcing it out, even when it has Ice Beam. If it wants to counter Latias with Sucker Punch, Payback, or Avalanche, it has to split its offensive EVs, making it less effective at everything-- IE, it's still easily countered. Honestly, I think it could go that route, but it wouldn't be as effective at that as it would at its intended purpose. I would say
allow Rain Dance as well given that.
Aqua Ring -
Disallow. The Magic Guard + Lefties + Aqua Ring combo possibility has already been mentioned, and I see this as too threatening / effective a form of recovery to allow.
Morning Sun -
Disallow. I don't care if it has lower PP or goes at half-power under Rain, SS, and Hail, it's a 50% recovery move otherwise and should therefore be banned like all the other 50% recovery moves.