Arcbound Slasher

Modular represents both a static ability and a triggered ability. “Modular N” means “This permanent enters with N +1/+1 counters on it” and “When this permanent is put into a graveyard from the battlefield, you may put a +1/+1 counter on target artifact creature for each +1/+1 counter on this permanent.”

If a creature has multiple instances of modular, each one works separately.

Riot is a static ability. “Riot” means “You may have this permanent enter with an additional +1/+1 counter on it. If you don’t, it gains haste.”

If a permanent has multiple instances of riot, each works separately.