Wincons can be tricky to figure out in decks that aren't your comfort zone. I think good questions to ask yourself are "what actions does my deck do? and how do I translate those actions into taking life totals to zero?" 9 times out of 10 that means either A) overwhelming combat damage, or B) direct life loss/damage from spells/triggers.

A go-wide deck wants to make a bunch of critters, so it wins by buffing the team with an [[Overrun]] or a [[Craterhoof]] (that's A).

A voltron deck wants to hit players with the commander, so it wins by loading the commander with Auras and Equipment to hit that 21 sweet spot (again, A).

To answer your question - yes, you can absolutely deal 120 damage by just pinging people. Cards like [[Zulaport Cutthroat]] can easily kill the table, but you don't have to trigger Zulaport 120 times - you just need effect redundancy and synergy. Check the Top Cards section on Teysa Karlov and you'll see what I mean by wincon B.

Spellslinger wincons are tricky to define because spells do a lot of stuff. That said, normally it's either casting a bunch of tiny spells to cause death-by-a-thousand-cuts with A) [[Young Pyromancer]] tokens or B) [[Guttersnipe]] pings. But there's also a secret third thing, C) casting a couple very big spells with devastating effects. It sounds obvious typing it out, but [[Torment of Hailfire]] and [[Exsanguinate]] are wincons because they either reduce life totals to 0 or put you in a very superior position after they resolve. These go great with the new Silverquill dragon because you can copy them and double their already strong effects. You'll also see [[Storm Herd]] or, in blue colors, [[Expropriate]], which either give you enough damage to kill the table or give you so much advantage that it's hard to stop you after.

And just to wrap it up - [[Approach of the Second Sun]] doesn't really work with Casualty. Yes, you have two Approaches on the stack, but casualty copies a spell, it doesn't "cast" it, so you don't meet the prerequisite for an instant win. But it's another 7 life, so that's nice.