Is Zog, Triceraton Castaway worth playing in Limited?

Yes, as a solid midrange body. A 5/4 with trample and reach for five mana is a good rate at common, and the enter ability helps push an attack through. Mountaincycling means it is rarely a dead card.

How does the enter ability work?

When Zog enters, you choose one target creature. That creature can't block this turn, so it can't get in the way of your attack. It does not tap the creature or remove it.

What does Mountaincycling do?

You pay two generic mana and discard Zog to search your library for a Mountain card, reveal it, put it into your hand, then shuffle. It is a way to fix mana or hit a land drop when the creature isn't useful.

Is this card legal in Commander and Modern?

It is a standard Magic card from the Teenage Mutant Ninja Turtles set, so it is legal wherever that set is legal, including Commander and Modern. Check the format list before a tournament, since legality can change.

Is this the foil or non-foil version?

This is the non-foil English printing, card number 111 in the Teenage Mutant Ninja Turtles set. Foil copies are a separate printing.

Does Zog work in a Dinosaur deck?

Yes. It is a Dinosaur Soldier, so Dinosaur tribal effects that count or buff Dinosaurs include it. Its red cost and Mountaincycling also fit red-heavy decks.