溶岩爪の辺境

溶岩爪の辺境はタップ状態で戦場に出る。
{T}：{B}か{R}を加える。
{1}{B}{R}：ターン終了時まで、溶岩爪の辺境は「{X}：ターン終了時まで、このクリーチャーは＋Ｘ/＋０の修整を受ける。」を持つ黒赤の２/２のエレメンタル・クリーチャーになる。これは土地でもある。

Lavaclaw Reaches

This land enters tapped.
{T}: Add {B} or {R}.
{1}{B}{R}: Until end of turn, this land becomes a 2/2 black and red Elemental creature with "{X}: This creature gets +X/+0 until end of turn." It's still a land.

Doctor Who

Ultimate Masters

Lavaclaw Reaches enters the battlefield tapped.
{T}: Add {B} or {R}.
{1}{B}{R}: Until end of turn, Lavaclaw Reaches becomes a 2/2 black and red Elemental creature with "{X}: This creature gets +X/+0 until end of turn." It's still a land.

A land that becomes a creature may be affected by "summoning sickness." You can't attack with it or use any of its {T} 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.

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