Psyduck - catchable in EVERY pokemon game but Leaf Green. If you play through all the games you will potentially encounter over a hundred psyducks. Psyduck is even in Areceus. Only magickarp and Magnemite appear in more games.

Charizard - catchable in TWO freaking games since gen one. You never even have to pick him.

Everyone - OMFG! Why is charizard everywhere?! Why does Nintendo shove this ONE pokemon down our throats?! WTF?!?! No other pokemon gets this treatment! Why are they obessed with this pokemon but no others?!

Me, a psyduck, in pic related.