Cannot be Normal Summoned while you control a monster. This card cannot declare an attack unless you control another Dragon-Type monster.
Rulings
Individual Card FAQs
If you have 2 copies of "Cave Dragon" on the field, they can both attack.
You can still Set, Flip Summon, and Special Summon "Cave Dragon" if there is another monster on your side of the field.
Netrep Rulings
If the only other Dragon-Type monster on the field is destroyed as a response to “Cave Dragon” declaring an attack, the “Cave Dragon"'s attack is stopped.
If “Skill Drain” is active on the field, “Cave Dragon” may still not be Normal Summoned if there are any other monsters on the field. If “Skill Drain” is active on the field, “Cave Dragon” may attack even if there are no other Dragon-Types on the field.
WIND|
Level 4|[ Dragon / Effect ]
ATK 2000|
DEF 100