Mythic Dungeons Scale by an Additional 30% Health and 15% Damage When a Mythic+ Key Starts

wowhead.com:

Whenever a Mythic+ key starts, all trash and bosses receive an undocumented 30% health and 15% damage buff from their Mythic 0 values in Season 3. Big thanks to Topher and Symfony for doing some investigation on this!

When we previously covered the Mythic+ Scaling in Season 3, we noted that the health pool of mobs has increased in Mythic+ dungeons from Season 2 to Season 3 by 46% or 5 keystone levels. This is still true, but how this scaling occurs is much different from previous seasons.

As with every season, the Mythic 0 dungeons are scaled by a base amount. For this Season transition, this amount appears to be 12% health, a much lower amount than previous Seasons. The base damage scaling is unknown at this time.

However, new to Season 3 is an undocumented buff which applies around a 30% health and 15% damage buff to all mobs from their Mythic 0 values whenever a keystone begins. This buff cannot be seen anywhere in game. In previous Seasons, the base Mythic 0 dungeons would receive the entire buff, which is usually around 3 to 4 keystone levels and the keystone scaling would handle the rest. This 30% health buff is about equal to previous Seasons as it's around ~3.5 key levels. However, combined with the base Mythic 0 scaling, this change results in the 46% health increase that we previously reported (5 keystone levels) when compared to Season 2. You can see this undocumented scaling easily on a +2 keystone, as this has keystone has a 0% keystone level modifier. This also applies to bosses. On a +10 difficulty, 883k (M0 health) * 1.3 (Tyrannical) * 1.85 (+10 Scaling) = 2.124 million. Multiply by another 1.3 for the hidden buff and you