If a deva uses its Change Shape ability to turn into a cat, what is its size?

Question

The Deva stat block states:

Change Shape. The deva magically polymorphs into a humanoid or beast that has a challenge rating equal to or less than its own, or back into its true form. It reverts to its true form if it dies. Any equipment it is wearing or carrying is absorbed or borne by the new form (the deva's choice).

In a new form, the deva retains its game statistics and ability to speak, but its AC, movement modes, Strength, Dexterity, and special senses are replaced by those of the new form, and it gains any statistics and capabilities (except class features, legendary actions, and lair actions) that the new form has but that it lacks.

According to the above, I believe if a deva used change shape to magically polymorph into a cat, it would have:

• Armor Class 12
• Speed 40 ft., climb 30 ft.
• STR 3 (-4)
• DEX 15 (+2)
• Lose its Darkvision
• Gain Keen Smell and Claws attack

However, would its size remain Medium or change to Tiny? If it maintained its Medium size, how would this effect the creature's appearance and game mechanics?

Also, let me know if I've missed anything regarding the stat changes.

Answer 1

Size is a game statistic (MM p.6)

It is not a statistic that is specifically called out by the exceptions in the Change Shape ability, however, it could fall into "it gains any statistics and capabilities (except class features, legendary actions, and lair actions) that the new form has but that it lacks" given that a size of Tiny is a statistic "that the new form has but that it lacks". Or, maybe not, because it already has a Size statistic.

So the answer is:

• Tiny, or
• Medium, or
• Deva's choice of Tiny or Medium.

Which of those is up to the individual DM.

As for how remaining Medium would affect its:

• appearance - it would be bigger than you would expect a cat to be. A Panther is Medium so - about that big.
• game mechanics - it would be Medium, not Tiny so it would take up a 5 by 5 ft. space instead of a 2\$1 \over 2\$ by 2\$1 \over 2\$ ft. (MM p.6).