The tame then breaks, but combat continues and the beast doesn't actually vanish or fade. No matter how many times you attempt to hit tame in a row it will repeat the shimmer thing.
What has been tried?
A heap of things have been tried, or considered, by Petopians on the PTR, including:
- Beating the stuffing out of it - no matter how low the creature's health it still resists taming.
- Hunter traps and stuns. Tar Trap, Freezing Trap, Concussive Shot and Binding Shot have been tried. Panthara will still avoid taming while stunned. SV Trap Mastery doesn't help.
- Flare.
- MM Sentinel power
- Track Hidden
- Countershot
- Tar Lord tar spit (in light of petrified panthara around them)
- Lighting a fire.
- Companion pet accessories: the two Pet Leashes, the Fetch Ball, and the Happy Pet Snacks don't work.
- Dragging them into the surrunding tar pits.
- Dragging them to under one of those strange, random yellow crystals about the place.
- The turnip gun toy won't work on enemies (idea was that painting it might prevent it camouflaging).
- Super Sticky Glitter Bombs prevent Rogues stealthing, but only work in Draenor.
- a bunch of repeated emotes: roars, pats, pets, growls
- lots of toys are hard to test since they didn't copy over to the PTR
- no sign of anything promising on the Army of the Light or Argussian Reach quartermasters
... I'll add more stuff when people remind me what they've tried.

If you have any ideas, or have tried other things, please mention them below. Are there any items that may produce bright light or mark the target in such a way that it can't be tamed?