This spell costs less to cast for each creature you control with a +1/+1 counter on it.
Creature spells you cast cost less to cast for each creature you control with a +1/+1 counter on it.
Hamza turns a wide board of countered creatures into a massive cost-reduction engine, letting you dump multiple fat creatures per turn. Early on you deploy cheap counter-generators, then snowball into overwhelming the table with discounted bombs and go-wide aggression. You win by flooding the board faster than opponents can answer, then closing with trample, anthems, or a big finisher.
Explosive midgame mana advantage that lets you cast several creatures in one turn
GW counters synergy is deep and well-supported with proliferate and anthem effects
Resilient go-wide boards that grind through removal
Self-reduces, so casting Hamza himself is rarely a problem
Board wipes are devastating since the strategy is creature-dependent
Cost reduction only applies to creature spells, leaving you weak to artifact/enchantment-based hate
No built-in card advantage engine in the command zone
Relies on having counters down first, so a slow start leaves Hamza expensive