The character gains a strength of 19  in bear or hybrid form only, and if his or her score isn't already higher, and a +1 bonus to AC while in bear or hybrid form (from natural armor).  in bear form only the were bears con is raised to 16, and if higher, their dex is lowered to 10.  Mental attributes remain the same, but in bear form the character cannot cast spells or speak.   The character may only cast spells in hybrid form if they successfully rolled to keep control of their actions. Attack and damage rolls for the natural weapons are based on strength.

Natural weapons in bear or hybrid form

Bite (Bear or Hybrid Form Only):  reach 5 ft., one target. Hit: 2d8 piercing damage. If the target is a humanoid, it must succeed on a DC 14 Constitution saving throw or be cursed with were bear lycanthropy.  After level 5 the character may add their strength modifier to damage  while in bear form, after level 10 in hybrid

Claw (Bear or Hybrid Form Only):  reach 5 ft., one target. 2d8  slashing damage.  After level 5 the character may add their strength modifier to damage  while in bear form, after level 10 in hybrid

Armor may generally not be worn through the transformation process, and lighter armor may be destroyed past saving.   Armor which fits the human form will generally not fit the hybrid form, which is 2-3 feet taller and nearly twice as heavy.  Heavy armor locked around the neck such as plate may pose a choking hazard at the discretion of the DM.

A shape shifted Wear-bear may use weapons or spells in hybrid, but not bear form

Involuntary transformation:

When injured below 30% health or truly and thoroughly enraged the werebear must roll against an involuntary transformation to hybrid or bear form.   Roll a Wisdom Save.  If the character beats a DC 12, they can retain control of their actions, but must still enter bear or hybrid form on a coin flip (heads hybrid, tails bear).  On a DC 14 they can retain control of their mind and if they enter bear or hybrid form as well.   On a DC 16 they can resist the transformation and remain in human form

On any full moon the natural born were bear must transform into hybrid or bear form, though they may roll a dc 15 wisdom save to retain control of their actions.  On a failed wisdom save the werebear will go on an uncontrolled rampage consistent with the normally good alignment of the were bear-- corrupt government officials may be mauled (and eaten), litter may be cleaned up (and eaten).  

The DM may also call for a save against involuntary bear at his or her discretion.

Voluntary transformation

Once per long the natural were bear may attempt a voluntary transformation to bear or hybrid form.   This requires a dc 12 wisdom check.   Failure results in remaining in human/elf form, though the transformation may be attempted again until successful.  Rolling a 1 results in a successful transformation, but loss of control for 1d4 rounds.

Upon finishing a voluntary transformation, the player takes a level of exhaustion.

At 5th level, the character may transform on a dc 5 wisdom check.   At 10th level, the player may transform twice per long rest, and does not suffer exhaustion for the first transformation.

On a voluntary transformation returning to human/elf form is a free action

They are resistant to non silvered non Magical damage.   In addition, non silvered non magical damage will lead to automatic success on a death save caused by said Mundane damage, though they will remain unconscious until healed.

Werebears are, at heart, always also bears, and will always have disadvantage on rolls for social interaction in urban areas or large crowds.  They will also always have disadvantage for wisdom saves involves food, and most are food aggressive, even in human form.

However, were bears will have advantage on doing bear like things-opening trash cans, fishing, so forth

A natural werebear can speak common and one other language which must be consistent with their humanoid  base race.  In Bear form they can communicate with bears, though given bears are not prone to diplomacy, this ability is generally the opposite of useful,

As Bears are--2 Cha, -1 dex in all forms.

Were bears are frigging Bears, though-- +1 str, +1 con

Werebears are vulnerable to silvered weapons, and silver in general, in all forms.   They dread formal dinner parties as a race. Casual contact with silver can cause up to 1d4 damage from casual contact.