Mill cards from your Deck with "Snake Rain" to be Special Summoned.
This card combos well with a number of other monsters:
"Spawn Alligator": Tribute the Summoned Reptile for "Spawn Alligator" and you will get it back for good during the End Phase.
"Code A Ancient Ruins": If you Summon an "Alien", Ancient Ruins will gain counters in the end phase.
"Offering to the Snake Deity": Since your monster is already doomed, destroy it prematurely to destroy your opponent's cards.
"Worm King" and "Worm Queen": After they have attacked, use their effects and Tribute them to destroy a card and Special Summon a new monster, respectively.
"Lion Alligator" and "Razor Lizard": Both require another Reptile-Type monster on the field for their effects. With "Viper's Rebirth", you can get the monster on-field in one turn.
"Solidarity": If you are using "Viper's Rebirth", chances are that you'll only be using Reptiles, so use "Solidarity" to buff your monsters.
"Reptilianne Gardna": You get to search a card from your Deck during the End Phase.