Any green deck worth its salt should have more than enough ramp to hit 9 mana before long, and tapping out for an entwined Tooth and Nail is guaranteed to make you a huge threat immediately
Vohar can do a serviceable impression of the classic Merfolk Looter, allowing you to sift through your deck while filling up your graveyard for later
High Perfect Morcant makes your opponents blight their creatures when elves enter the battlefield, while using those same elves to proliferate
Both of these cards can make Glorybringer struggle, getting the better of Glorybringer in different ways, mana and survival, respectively
Phyrexian Dreadnought ($278) Phyrexian Dreadnought has a very real drawback, so it's not something to just jam in a deck because any deck can cast it
While there are a plethora of Summon cards to suit various types of decks, a deck dedicated to summoning and summoners is viable in its own right