Can modular monstrocity only name one-word keywords (lifelink, prowess, undying), or also ones with modifiers, like annihilator 6, swampwalk, protection from everything, cumulative upkeep - add R, outlast W, etc.?

No, it can name any keyword regardless of word length. It just has to have been printed in a creature card.

So I'm not sure who designed/developed outlast, but I feel like it was super unintuitive, when I first read it, it took like 3-4 try to understand the ability, and every time I read it it got worse. Sorcery speed and summoning sickness killed it.

When we have to chose between how intuitive something is and how good the gameplay is, we err towards good gameplay.

Can you give some past mechanics that had really small design space?

Cipher is the one that jumps to mind. Outlast is another.

Would Outlast have fared better if it allowed you to target any creature you control?

It’s not New World Order and lacks flavor, so I’ll say no, it wouldn’t have fared better.

Not that I disagree with your decisions, but I think the asker meant why so many keyword abilities use only as a sorcery. Outlast, Unearth, Scavenge, Level Up, Equip, Transfigure,

Those are gameplay decisions. Read my “Choices vs. Options” article.

MaRo, why is it that the abilities Level Up and Outlast are only allowed at sorcery speed? They don't seem too strong at instant speed. Is it to weaken control?

Making them instant significantly increases their power level (forcing us to charge more) and lessens meaningful strategic decisions as the correct play is almost always to wait and react in response to threats.

Just listened to one of your podcasts from April 2013, "Instants and Sorceries", and you talked about Morph and the importance of not making everything doable at instant speed (Outlast). It's fun to know what you were working on when u recorded.

There is all sorts of secrets hidden within my writing and podcasts. : )

I like how the Tarkir mechanics all kinda work with each other. Exploit gives you Delve fuel. Rebound doubles the Prowess triggers. Casting a card for a dash cost means you'll likely be attacking, which sets up the requirements for Raid. Then the Abazan and Temur is were it falls apart. Outlast kinda lets you control how you bolster. Ferocious and Formidable really are the same thing, different requirements.

Bolster puts +1/+1 counters on you creatures (as does outlast) and both are rewarded by +1/+1 enablers (many of which are outlast creatures).Ferocious and Formidable require the same dedication to creatures and thus can go in the same deck.

I understand you couldn't have outlast and raid in Fate Reforged for story/ space reasons. But why couldn't you do 50/50 split between outlast/Bolster or Raid/Dash in FTF? That way when drafting Dragon of Tarkir you can still play with Outlast or Raid?

There is just so much space in a small set.

Would you have considered making white Dash cards in FRF or KTK if the set really needed it, in the vein of blue Exalted, black Outlast, and other mechanics that have bled the pie? Or would that have gone too far?

The overall structure supersedes individual cool card designs.