A completely new class!
Let's make a little chart using the four base values each champion has (damage, utilty, mobility, tankyness) and what roles differant combinations make.
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High Stats
Utility, Damage, Tankyness and Mobility-
Damage and Mobility- These are your Assassins
Damage and Tankyness- Your Bruisers
Damage and Utility- The Mages/ADC's
Utility and Tankyness- The Tanks
Utility and Mobility- ?
What if there was a new breed of Champions which used mobility and stealth mechanics to unleash fight changing lockdown and disruption? Low health targets are often associated with compensating with high damage, but what if this class had scaling cc and low ability scaling? A talon appears in your backline and pops your adc before escaping, changing the fight. In a similar way this class would pop up or dash in to unleash hellish suppression, debuffs, and disruption before exiting the carnage.
The Suppressor class.
Yes they'd need to buy this one specific item to counter that champ,but it would pretty much nullify the sole purpose of him/her.
and
for example... Not enough gold to build damage but enough inherit cc in their kits to heavily effect lane and team fights.