Cold-Eyed Selkie is in the precon to highlight this strategy
Unfortunately its difficult to build around and not particularly interesting or powerful once you tick all of these boxes
Second of all, which deck(s) would be the best choice(s) to take to a real tournament
There are so many green cards that help make extra mana, find lands from your deck to put them into play, or turn your creatures into lands, or do something else that somehow produces mana, that it's simply impossible to list them all
With the trigger to deal four damage on both entering the battlefield and attacking, giving Boilerbilges haste with cheap effects from cards like Lightning Greaves can let you deal up to 13 damage
In these decks it is missing the fourth land drop that is often fatal however it is rare to be throwing back three land hands and it is in finding that 4th land that Oracle shines