Its second-best feature is to double the triggers from the doctors abilities, so The Tenth Doctor can get plenty of Allons-y triggers, while The Ninth Doctor can get an extra upkeep, and so on
They prefer to keep it in house
Taurean Mauler Honorary Spider There are not actually a ton of Spiders in mono-red, so you will likely have to rely on creatures with changeling to fill the Spider quota
On top of that, during each of your upkeeps, it distributes +1/+1 counters among your dragons by color, and if you manage to hit all five colors, you just win the game
It pairs perfectly with cheap artifacts like Ornithopter and Mishra's Bauble, making it a natural fit for any token-fueled Affinity strategy that wants to snowball board presence