He maintains the Menace ability, and grows to become a 7/7
The ninjutsu ability can be activated during the declare blockers step, combat damage step, or end of combat step
It's easy to identify these doppelgngers, though - just look at the cards in the decklists
With the right mix of creatures and token-makers, your opponents will struggle to handle the volume of -1/-1 counters heading their way, making it hard for their own creatures to take a foothold and deal any meaningful damage
If its a scalper or a five-year-old buying the products, the money fills up their bank just the same
Also, if the bots get updated you will need to be flexible and able to identify the new tendencies, which can either be viewed as a fun new challenge or an inconvenience