Undergrowth Champion

• WWizards of the Coast2015-08-25
  Official Ruling
  If damage that can't be prevented is dealt to Undergrowth Champion while it has a +1/+1 counter on it, you'll still remove a +1/+1 counter on it.
• WWizards of the Coast2015-08-25
  Official Ruling
  If Undergrowth Champion is dealt damage from multiple sources at the same time (for example, if it's blocked by multiple creatures), its prevention effect will apply once to all that damage. You'll remove only one +1/+1 counter.
• WWizards of the Coast2024-11-08
  Official Ruling
  A landfall ability triggers whenever a land you control enters 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.
• WWizards of the Coast2024-11-08
  Official Ruling
  Whenever a land you control enters, 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 (As a result, you can have those abilities resolve in the order of your choosing.).
• WWizards of the Coast2024-11-08
  Official Ruling
  A landfall ability doesn't trigger if a permanent already on the battlefield becomes a land.

Rulings via Scryfall