Saproling Madness

[Pi]

{sprout swarm} and a {concorand crossroads} or {ferver}, {fires of yavamia} and 3 or more token doubling enchantments {parallel lives} or {doubling season}.
You need 5 mana and/or creatures to cast sprout swarm once and buy back, then you double your token 3 times (octuple), make sure your tokens get haste and then use 5 of your new saprolings to make more saprolings.

Edit: convoke does not care about summoning sickness, you just need untapped creatures

702.50a: Convoke is a static ability that functions while the spell with convoke is on the stack. "Convoke" means "For each colored mana in this spell's total cost, you may tap an untapped creature of that color you control rather than pay that mana. For each generic mana in this spell's total cost, you may tap an untapped creature you control rather than pay that mana." The convoke ability isn't an additional or alternative cost and applies only after the total cost of the spell with convoke is determined.
Example: Heartless Summoning says, in part, "Creature spells you cast cost {2} less to cast. You control Heartless Summoning and cast Siege Wurm, a spell with convoke that costs {5}{G}{G}. The total cost to cast Siege Wurm is {3}{G}{G}. After activating mana abilities, you pay that total cost. You may tap up to two green creatures and up to three creatures of any color to pay that cost, and the remainder is paid with mana.

[Munchlax]

You don't even need a haste proc. the card allows you to tap them. It is not their own tap ability.

[Subiskier]

I thought you couldn't tap a creature first turn even if it's for a different creature's ability. Ruling?

[Munchlax]

I thought you couldn't tap a creature first turn even if it's for a different creature's ability. Ruling?

I don't know the exact ruling. Sorry but I know it works.

[particle]

I thought you couldn't tap a creature first turn even if it's for a different creature's ability. Ruling?

there was a rules question recently about convoke with this. the point is, you cannot activate an ability of a creature that says "tap: x results" if the creature has summoning sickness. however, if the creature had an ability similar to {arachnus spinner} with an ability that said something like "tap an untapped creature you control: results in x" any of your untapped creatures can be used to pay for this ability, regardless of summoning sickness. similarly, creatures can be tapped for convoke the turn they enter since its an alternative cost, not them using their own specific tap ability.

[Subiskier]

I was at an FNM, {captivating vampire} and three other vampires on the battlefield. I played a fifth vampire and tried tapping it with the others to steal an opponents creature and judge said it didn't work. Can't tap a new creature to another ability. So now I'm confused. Was he wrong?

[particle]

I was at an FNM, {captivating vampire} and three other vampires on the battlefield. I played a fifth vampire and tried tapping it with the others to steal an opponents creature and judge said it didn't work. Can't tap a new creature to another ability. So now I'm confused. Was he wrong?

bad judge, bad. jk but yea you can tap vampires that are summoning sick for {captivating vampire}'s ability.