Nice work. #1 is good to know, but you should test if a faster Mischievous Whirlwind user moves before a slower Counter user and if a slower Mischievous Whirlwind user moves before a faster Counter user before you nail it down to exactly one priority level in all cases. Also, can a fast Mischievous Trick Room user go before a slow non-Mischievous Whirlwind user, etc. Once we test this, I'll move it from tentative to confirmed.
The_Chaser and I just finished testing these.
1. Fast Weavile Counter vs. Medium Speed Murkrow Whirlwind
Result: Fast Weavile Counter went before Whirlwind
2. Slow Wobbuffet Counter vs. Medium Speed Murkrow Whirlwind
Result: Medium Speed Murkrow Whirlwind went before Counter
3. Fast Erufuun Trick Room vs. Slow Skarmory Whirlwind
Result: Trick Room went before Whirlwind
Considering each move's priority (Trick Room = -7, Whirlwind = -6, Counter = -5), I think this makes it fairly conclusive that Mischievous Heart adds exactly +1 priority to all non-attacking moves.
We also tested Mirror Move more:
Whoa, hold on there. I think we're a long way from drawing conclusions about how Mirror Move works. In 4th gen, it was probably the most complicated move in the game, and its implementation has changed yet again in gen 5.
When you say that it fails against a regular-priority move, what move was that, Roost? Mirror Move doesn't replicate Roost because Roost doesn't target the Mirror Move user. And if it was an actual attack, did the Mirror Move user still fail to replicate the move on the following turn?
Since the first time we did this, we had to use U-turn, Mirror Move failed. It only worked when a faster priority attack hit the Mischievous Heart Mirror Move Pokemon. To test it further, we did the following test:
1. Murkrow Mirror Move vs. Machop Strength
Result:
Turn 1
Murkrow used Mirror Move! But it failed!
Machop used Strength! Murkrow takes the hit!
Turn 2
Murkrow used Mirror Move! Murkrow used Strength! Machop takes the hit!
Machop used Strength! Murkrow takes the hit!
Turn 3
Philip7086 switched Machop out! Philip7086 sent out Skarmory!
Murkrow used Mirror Move! But it failed!
Drawing from these results, and the results we got from testing Mirror Move against Extremespeed (Mirror Move succeeded on turn 1, after being hit by Extremespeed first), I think we are close to a few conclusions. It seems Mirror Move needs a few criteria to be met for it to function (in singles battles):
1. The Mirror Move Pokemon must have taken a hit directly before using Mirror Move
2. The Mirror Move Pokemon must be targeting the same Pokemon who targeted it for Mirror Move to work
Next, The_Chaser and I tested Healing Heart, as requested in the OP:
Healing Heart: What are its chances of activating every turn? Does it act like Heal Bell, healing all members of the team, or does it heal only one at a time?
Okay, so I used a Rotom with the moveset, Will-o-wisp, Thunderwave, Toxic, and Shadow Ball, and spent the first part of this test statusing multiple members of The_Chaser's party, including Tabunne, the Healing Heart Pokemon. Then, for 30 turns, I kept using Shadow Ball and other moves against Tabunne to see how often it would heal its teammates of status attacks. Out of these 30 turns, Tabunne did not heal a single member of it's party of status even ONCE. We then tried to see if Tabunne heals status moves while not active in the battle. We tested this for around 15 turns while Tabunne was not actively in the battle, and again, not a single Pokemon was healed of its status.
From this test, either we can conclude that The_Chaser and I are the unluckiest people on the planet, or that Healing Heart has an incredibly low activation rate, or that Healing Heart is more of an in-game mechanic, where if you're running around with a Healing Heart Pokemon, your other Pokemon's statusses might be healed. We will try testing this again later today when I get some more time.