Thats not quite the case with Karns first appearance as a creature, however, as its Urzas Saga debut wasnt exactly heralded an the over-powered entity the character is historically considered
Dreadhorde Invasion can also eventually provide a bit of lifegain, although your deck will need to be specifically tailored for that: Your odds of growing an army to 6/6 with only Dreadhorde Invasion are very slim
In Modern, the first one is on the banlist for its sins when paired with Not Dead After AllNot Dead After All and the latter is a staple interaction of the format
One thing I am pretty glad that I didnt crack is Broodbirth Viper because I have a playset of those
If you don't, create a 1/1 blue Fish creature token
The ability to give Rats menace would be solid enough, but it has the extra bonus of being able to make more Rat tokens and steal your opponents' creatures