Restricting your deck to only mono-blue spells removes options, but you can funnel all that mana into blue card draw spells to trigger the likes of Psychosis Crawler and Ominous Seas to bury your opponents in card advantage, damage, and triggers
Other cards have similar effects, like Tidal Barracuda giving it to the entire table, but starting the game with a Leyline of Anticipation out is an incredible way to get way ahead of the game
Groundchuck & Dirtbag Groundchuck & Dirtbag is far from the flashiest card to slap in the command zone, but it has a fundamentally green flavor: Its a big creature that enables bigger plays, whether you open a portal to Magics greatest foe or summon eldritch horrors from beyond reality
It also has trample, which is the natural downside missing from many giant creatures
Emrakul and Chatterfang For a long time, Magic players have joked that Emrakul cant be that strong if she can be beat by 15 squirrels
Mazemind Tome