Here is an example of a Stoat hunting a Rabbit 10 times it's size: http://www.youtube.com/watch?v=HNbqvqf3-14
As you can see, these animals are very funny but can be very deadly at the same time. Now, let's move onto abilities.

Play Fight
- Instant
- 2 Minute Cooldown
You and your Mustelid have a play fight, increasing your attack and haste by 5% for 2 Minutes.
Or...

Predatory Stamina
- Instant
- 5 Minute Cooldown
Every time your Mustelid is hit with a critical hit, it's Stamina goes up by 5%. Stacks up to 6 times.
Or...

Sneak Attack
- Instant
- 3 Minute Cooldown
Your Mustelid disappears from sight, but then suddenly strikes without warning in a random location. When it strikes, your Mustelid deals nature damage to the target.
Or...

Musk
- Instant
- 3 Minute Cooldown
Your Mustelid sprays Musk on any attackable target behind it. Once sprayed, the targets run away in fear. If the targets sprayed do not go into a body of water, they will fear any allies near them.
And that is my idea, for tamable Mustelids. If you have any suggestions, you can post them.