Obuun, Mul Daya Ancestor

At the beginning of combat on your turn, up to one target land you control becomes an X/X Elemental creature with trample and haste until end of turn, where X is Obuun's power. It's still a land.
Landfall — Whenever a land you control enters, put a +1/+1 counter on target creature.

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At the beginning of combat on your turn, up to one target land you control becomes an X/X Elemental creature with trample and haste until end of turn, where X is Obuun's power. It's still a land.
Landfall — Whenever a land enters the battlefield under your control, put a +1/+1 counter on target creature.

A landfall ability doesn’t trigger if a permanent already on the battlefield becomes a land.

A landfall ability triggers whenever a land enters the battlefield under your control for any reason. It triggers whenever you play a land, as well as whenever a spell or ability puts a land onto the battlefield under your control.

Effects that modify the power or toughness of the land creature without setting it will apply to its new base power and toughness no matter when they started to take effect. The same is true for counters that change its power and toughness.

Obuun’s first ability can target a land that’s already a creature. This overwrites any previous effects that set the land creature’s power and/or toughness to specific values. Other effects that set these characteristics to specific values that start to apply after the ability resolves will overwrite that part of the effect.

Obuun’s first ability doesn’t remove any abilities the land creature has.

Whenever a land enters the battlefield under your control, each landfall ability of the permanents you control will trigger. You can put them on the stack in any order. The last ability you put on the stack will be the first one to resolve.