Other Goblins get +1/+1 and have mountainwalk.

When Muxus enters, reveal the top six cards of your library. Put all Goblin creature cards with mana value 5 or less from among them onto the battlefield and the rest on the bottom of your library in a random order. Whenever Muxus attacks, it gets +1/+1 until end of turn for each other Goblin you control.

Exile this card from your hand: Add {R}.

Nonbasic lands are Mountains.

{T}: Create X 1/1 red Goblin creature tokens, where X is the number of Goblins you control.