I do, sometimes.

Mascot is a sub-standard or obsolete creature card. Just 1 in main or SB - sided-in in unwinnable matches.

Some typical examples:
Pearled Unicorn
Ironroot Treefolk
Dwarven Warriors
Scavenging Scarab
Storm Crow
Coiled Tinviper
etc.

Surprisingly, it works sometimes out of pure luck. Also, there is the WTF factor: opponent can't believe what he is playing against and feels uncomfortable about possible loss.