For example, Exodia decks with mostly Normal Monsters can use Heart of the Underdog to extend your Draw Phase, increasing the chance of drawing Forbidden One cards
Running 3 copies of many of his most important combo cards allowed him to more consistently draw into the cards he needed to win
For the rest of this turn, unless this effect was negated, you cannot Special Summon, and any battle damage your opponent takes becomes halved
Remove a +1/+1 counter from Spike Feeder: You gain 2 life
Hitting one land per opponent when youre already at six mana is unlikely to make a difference, so that mode isnt great either
If the taught creature leaves the battlefield, Pyromancy 101 will stay exiled but won't be taught to any other creature