Wandering Fumarole

Because damage remains marked on a creature until the damage is removed as the turn ends, nonlethal damage dealt to a creature may become lethal if you switch its power and toughness during that turn.

Effects that switch a creature's power and toughness apply after all other effects, regardless of when those effects began to apply. For instance, if you target a 1/2 creature then give it +2/+0 later in the turn, it's a 2/3 creature, not a 4/1 creature.

Switching a creature's power and toughness twice (or any even number of times) effectively returns the creature to the power and toughness it had before any switches.

A land that becomes a creature may be affected by “summoning sickness.” You can't attack with it or use any of its abilities (including its mana abilities) unless it began your most recent turn on the battlefield under your control. Note that summoning sickness cares about when that permanent came under your control, not when it became a creature nor when it entered the battlefield.

An ability that turns a land into a creature also sets that creature's power and toughness. If the land was already a creature (for example, if it was the target of a spell with awaken), this will overwrite the previous effect that set its power and toughness. Effects that modify its power or toughness will continue to apply no matter when they started to take effect. The same is true for counters that change its power or toughness (such as +1/+1 counters) and effects that switch its power and toughness. For example, if Wandering Fumarole has been made a 0/0 creature with three +1/+1 counters on it, activating its last ability will turn it into a 4/7 creature that's still a land.

This land is colorless until the last ability gives it colors.

When a land becomes a creature, that doesn't count as having a creature enter the battlefield. The permanent was already on the battlefield; it only changed its types. Abilities that trigger whenever a creature enters the battlefield won't trigger.