Here are some highlights of what's to come in 5.4. Keep in mind that these patch notes are subject to change over the course of the PTR.
- A new pet battle tournament is available on the Timeless Isle, more details coming soon!
- Players are now able to trade in any 3 of the same family specific Flawless Battle-Stones for a single Marked Flawless Battle-Stone.
- Aquatic type's passive effect now reduces damage from damage-over-time effects by 50%, up from 25%.
- Critter type's passive effect now makes critters immune to roots, stuns, and sleep effects.
- Dragonkin type's passive effect now activates after an attack brings a target's to below 50% health, up from 25%.
- Elemental type's passive effect now only affects negative direct effects of weather. (E.g. Sandstorm's accuracy reduction won't be applied, but the damage reduction will.)
- Magic type's passive effect now caps damage taken at 35% of maximum health, up from 40%.
There are also some adjustments to a few pet abilities as well as two UI updates. Check out the full list of changes here.
In addition to the official patch notes, Wowhead discovered four new possible pets coming in 5.4. [source]
- Crafty (Bind on Pick Up)
- Moon Moon (Bind on Equip)
- Rascal Bot (Bind on Pick Up)
- Essence of Xuen (Bind on Pick Up)
Last but not least, Wowhead datamined a new Darkmoon Faire world boss. This newest addition seems to be a direwolf and may drop a few special items, including the pet Moon Moon! [source]