Flickering creatures, a subset of whites protective magic, or reanimating them from the graveyard can often create a loop, while whites many defensive abilities can create soft locks that leave it invulnerable unless removed
In this list, well be focused on generically good ramp cards
Magics designers must have underestimated the power of delve, because when the Khans of Tarkir set released, several of its cards were soon banned from several formats due to being too powerful
A card like [mtg_card]Satyr Wayfinder[/mtg_card] (included in the precon) is a great example of what shes looking for: it has a good ETB trigger, it dumps new cards into your graveyard, its not a loss to sacrifice it, and it has a low mana cost, so you can start bringing it back right away
There might be a line over which things are obviously not casual, but the other side of that line is a sliding scale which is part of the issue leading to mismatched expectations and why we want to have more productive conversations about it
it's one of the strongest colorless ETB effects in the game
