I had ideas for a few ceno hybrids like Phorusrhacos + Enteledon: Entrhacos or Phorusteledon. It would be mainly Phorusrhacos with hoove like feet and a furry mane on its back. It would be plains obviously.
Another idea was the Deinotherium + Diprotodon: Diprotherium. It would be mainly Diprotodon with Deinotherium tusks and the beginnings of a trunk. It would be snows obviously.