Don't buy Aghs...

We're not in 6.81 anymore, their two Aghs used to suck but they got huge buffs since then.

Aghs Puck is absolutely core as the game goes late, it's one of the very rare ways to have a decent late game with Puck actually. Every competitive team builds Aghs on Puck. It has one of the best synergies with any kind of AOE damage like Gyro/Dusa/Ember because nobody can escape the coil. 4.5 second BKB piercing stun, 'nuff said.

Aghs OD, well, it kind of mana drains an entire team, it's also pretty good. Tidehunter without mana? Medusa without mana? You get the idea. Definitely very situational but there's no way it's a bad item.

Infinite bounces is amazing IF your team has enough lockdown/grouping to really let it rip with rapid, close range bounces, but generally it's hard to land even the full 10 against a competent team - hence the Veil which makes it hit a lot harder, and also amplifies anything else your team is throwing out. It's pretty good for survivability too.

Kinda know where you're going with the Blink Dagger hamster - any good team will focus the hell out of you, and it lets you counter-initate at the right moment. Decent escape obviously, but not sure how much else he gets out of it (blinking in and landing a slow < blinking in and landing a stun). You can sometimes achieve the same result with a Smoke of Deceit.

Nigma I like my Refresher Orb, but Aghanim's Scepter is niiice too. I think he's a bit like Tinker - his Agh's is pretty good too, but you have a lot of other things which you need/might be better.

Veil of Discord I'd say is more important than Aghs on Lich, I might still pick it up afterwards if your team has a lot of lockdown, otherwise you might be better with something else.

Would say get it get it get it on:

AA, Omniknight, Enchantress, Clockwerk, Disruptor, Tiny, Treant Protector Puck, Invoker.

Strongly worth considering on:

Abaddon, Chen, Huskar, Dark Seer (if late), Lion, Lina, Necrophos, KOTL, Pugna, Razor, Silencer, Shadow Shaman, Juggernaut (CD alone), Zeus, Enigma, Beastmaster, QoP, Night Stalker Brewmaster (maybe), Crystal Maiden, )

I probably missed a few, meh.