The iframe, line by line

src

Always https://unlatchgames.com/play/<game>/?pub=<your code>. The game id is the folder name — the catalogue lists them all.

The ?pub= is not optional. Without it the page loads as our own site, header and all, and will refuse to render inside your page.

allow="autoplay; fullscreen"

Games make sound on a tap, never on load, so autoplay permission is only needed for the first sound after that tap. Without fullscreen the games that offer it cannot go fullscreen from inside your page.

allowfullscreen

The older spelling of the same thing. Harmless, and still needed by some browsers.

loading="lazy"

Worth keeping if the game is below the fold. A game is a few hundred kilobytes; not fetching it until someone scrolls to it is free.

title

Not decoration. A screen reader announces an iframe by its title, and an untitled one is announced as "frame".

What about sandbox?

You do not need it, and if you add it the game will stop working unless it includes at least allow-scripts allow-same-origin. The games run entirely in the browser, keep their progress in their own origin, and never navigate your page.