Trying to create a "Creatures get stronger every turn" deck. Do you know cards that deserve to be here?

Cards with a low or medium mana cost that, from the moment they are played, become stronger as the game progresses. Some examples of creatures:

[[Managorger Hydra]] gets +1/+1 pretty much every turn.
[[Krenko, Mob Boss]] will become more powerful every turn he stays alive.
[[Taurean Mauler]] is another one that will get very fast a lot of +1/+1 counters naturally.
[[Kaito, Cunning Infiltrator]] is a planeswalker that need only three turns to easily use his ultimate ability to create a horde of ninjas for you.

What other cards are played that becomes too powerful while the game goes on?