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We are working on a cute monster with a big tongue:

We want the tongue to have a different material and texture than the rest of the body. We also want to rig the tongue so it elastically stretch from the soft palate when the mouth opens.

We are discussing two strategies concerning the tongue:

1. The tongue is a part of the main body mesh. We control how the bone flexes the body using weight paint. Applying the textures requires careful separation between the body and the mouth.


2. The tongue is a separate object from the body. This strategy seems more logical, as the tongue is indeed something different like the leg is different from the torso. Applying the textures and sculpting will be easier, but we have doubts about how to animate opening the mouth, which involves both flexing the body and stretching the tongue out.


3. The tongue and the lower soft palate is a separate object. Upper soft palate is a part of the body, because it needs to move and stretch when the jaw opens. It seems like a compromise, but it may well be the most difficult to achieve and tune.

Questions:

1. Are those options equally feasible, or is one more manageable than the other?


2. If option 2 has some merits, how to reliably parent the soft palate and tongue to the body, so it stays connected when the upper jaw (part of the body) opens? Comment below the answer this question suggests that it may not be possible:character made with multiple objects one armature or different armatures
   

All the options are equivalent in terms of animation comfort (user interacts with armature only), how they deform (separate or not, the weight painting of vertices can be the same) and materials (you can assign materials to individual faces).

A reason to split your mesh in rigging is to be able to interactively hide parts of it (but this can be also done with mask modifiers on the mesh), or to be able to split it (dismember body parts,..). None apply here.

There are no issues with one armature driving multiple meshes. You can even pack everything up into a group and link it as a single entity with a proxy rig that drives that.

In terms of setting the rig up, having the mesh in one piece is the most convenient, because you have the ability to blend weigh-painting well between bones.

Options 1 and 2 can both easily meet your needs, while option 3 can lead to bad performance in the joining zone.

In option 1, you can assign to the tongue a different material and textures, or even have a single material divided by UV unwrapping and careful texturing.

In option 2 there is no problem having two different objects controlled by a single bones rig, which will also perform the parenting between spare parts.

Just remember to parent both meshes to the rig, and I would suggest to use "with empty groups" instead "automatic weighting"; then set your rig display as "X rays" go to pose mode, select the body mesh, switch to weight paint mode, select all the body bones, press W "assign automatic from bones", do the same with the tongue and you will have a good starting point to be trimmed.