General Combos
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The deck runs many combos. In fact, it's not that unusual to accidentally assemble one of them by just randomly flipping cards with Grenzo.
Here's the list:
Murderous Redcap - Skirk Prospector/Ashnod's Altar/Viscera seer - Metallic Mimic
Here, you sacrifice Murderous Redcap so that it will come back to play because of persist, but the -1/-1 counter will be elided with the +1/+1 counter granted by Metallic Mimic. You can repeat the process infinite times, shooting everybody to death with Redcap's triggered ability.
Kiki-Jiki, Mirror Breaker - Skirk Propector/Ashnod's Altar/Viscera Seer - Lightning Crafter
This combo requires 3 cards but can win at instant speed, since it relies on direct damage and doesn't need to pass through the combat phase.The combo works as follows: you copy Lightning Crafter with Kiki-Jiki, the token champions Kiki-Jiki, then you tap it to deal 3 damage, then sacrifice the copy of Lightning Crafter. Kiki-Jiki returns to play untapped, so that you can repeat the process as many times you want until you kill everybody.
Goblin Recruiter - *Goblin Warchief/Chieftain* - Conspicuous Snoop - Kiki-Jiki - Sling Gang Lieutenant
This combo takes two turns with a haste enabler on the field, otherwise it takes three turns due to summoning sickness.
- Cast Goblin Recruiter with Warchief or Chieftain on the field.
- Search your library for Conspicuous Snoop, Kiki-Jiki, and Sling Gang Lieutenant, and put them on top of your library in that order.
- Draw and cast Conspicuous Snoop the next draw step.
- Activate Conspicuous Snoop using the ability gained due to Kiki being on the top of your library by tapping Conspicuous Snoop, creating a token copy of itself.
- Repeat for infinite tapped token copies of Conspicuous Snoop.
- Activate your untapped token copy to Conspicuous Snoop by tapping it, creating a copy of Goblin Recruiter.
- Goblin Recruiter enters the battlefield, searching your library for Sling Gang Lieutenant and putting it on top of your library.
- Sacrifice an arbitrarily large number of Conspicuous Snoop tokens using the ability gained due to Sling Gang Lieutenant being on top of your library for an arbitrarily large amount of life loss.
Grenzo - The Cauldron of Eternity - Skirk Prospector/Ashnod's Altar - Murderous Redcap
This combo is very straight forward, continue to sacrifice Redcap who goes to the bottom of the library. With the mana generated with Ashnod's Altar, return him to the battlefield with Grenzo's ability. Since both triggers from Persist and Cauldron happen at the same time, you can choose which ones to order (persist happening before Cauldron), allowing for the full two possible mana from Skirk Prospector.
Grenzo - Goblin Warchief/Chieftain - Skirk Propector/Ashnod's Altar - The Cauldron of Eternity - Krenko, Mob Boss
This combo is similar to other Cauldron combos. Sacrifice Krenko (and possibly some tokens) to a mana outlet to put him on the bottom of your library. From there, return Krenko to the battlefield with Grenzo with a haste enabler to create infinite tokens. A haste enabler for all goblin tokens will allow for winning that turn.
Maralen of the Mornsong + Stranglehold
This isn't technically a combo, since you're not winning right away, but if it gets unanswered your opponents will be prevented from drawing new cards for the rest of the game. Also, it could be considered a 1-card combo, since you only need to flip Maralen and she will tutor for Stranglehold by herself. Therefore, it's a good pile for Insidious Dreams. If you have both cards in play, on your turn you'll pay 3 life to tutor for whatever, on other players' turn they'll still pay 3 life but can't search for anything because of Stranglehold. As I said before, Maralen has to hit the battlefield just before your draw step for this to work. Additionally, make sure to have 3R mana open to cast Stranglehold on that same turn.
Doomsday Pile
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Here I will detail some notable piles you can stack with Doomsday.
It's important to note that they're meant to be a guideline and not an exhaustive list. In fact, sometimes you could have some combo pieces already on the battlefield (or in your hand), other times you could have more or less mana available for extra protection and so on. You should adapt them to the game situation.
Cards are listed in the order they would be flipped by Grenzo, i.e. the first card will go on the bottom and the last on top of your library.
Doomsday - Grenzo - Priest of Gix - Kiki-Jiki, Mirror Breaker - Murderous Redcap - Skirk Prospector - Metallic Mimic
(This pile requires 2BBB mana available.)
Cast Doomsday and put Priest, Kiki, Redcap, Prospector and Mimic from the bottom in order listed.
Pay 2 mana to flip Priest of Gix and net 3 black mana in exchange.
Use 2 of those 3 mana to flip Kiki-Jiki, Mirror Breaker, tap it to copy Priest of Gix and net 3 more black mana (4 total).
Use 2 of that mana to flip Murderous Redcap, shoot whatever you want for 2 damage.
Use the last 2 mana to flip Skirk Prospector, then sacrifice Kiki-Jiki and the Redcap to net 2 red mana.
In response to Redcap's persist trigger, use that mana to flip Metallic Mimic.
Murderous Redcap will return to the battlefield with no counters, so you can go infinite.
Doomsday - Grenzo - Zealous Conscripts - Goblin Lord - Kiki-Jiki, Mirror Breaker - Priest of Gix
(This pile requires 2BBB mana available.)
Cast Doomsday by paying BBB, searching your library and graveyard for one any other card, Zealous Conscripts, Goblin Sledder, Kiki-Jiki, and Priest of Gix, exiling all other cards from your graveyard and library, and then placing the remaining cards on top of your library in the order previously listed and losing half your life, rounded up.
Activate Grenzo by paying 2, putting Priest of Gix into your graveyard and then onto the battlefield, adding BBB.
Activate Grenzo by paying 2, putting Kiki-Jiki into your graveyard and then onto the battlefield.
Activate Kiki-Jiki by tapping, creating a token copy of Priest of Gix.
Token copy of Priest of Gix entering the battlefield, adding BBB.
Activate Grenzo by paying 2, putting Goblin Sledder into your graveyard and then onto the battlefield.
Activate Goblin Sledder by sacrificing it, giving Grenzo +1/+1 until end of turn.
Activate Grenzo by paying 2, putting Zealous Conscripts into your graveyard and then onto the battlefield, untapping Kiki-Jiki.
Activate Kiki-Jiki by tapping, creating a token copy of Zealous Conscripts.
Doomsday - Grenzo+1/0 - Kiki-Jiki - Sling-Gang Lieutenant - Goblin Hastelord - Conspicuous Snoop - *Random Card*
(This pile requires 4BBB or 6BBB available.)
Cast Doomsday by paying BBB, searching your library and graveyard for Kiki-Jiki, *Random Card*, Sling-Gang Lieutenant, Goblin Hastelord and Conspicuous Snoop and placing them on top of your library in the order listed.
Activate Grenzo twice, putting Conspicuous Snoop and Goblin Hastelord into your graveyard and then onto the battlefield.
Active Conspicuous Snoop using Kiki-Jiki's ability by tapping it, creating a token copy of Conspicuous Snoop with haste.
Repeat with the new Conspicuous Snoop token an arbitrarily large amount of times. *if Priest is in stack, copy with last activation*
Activate Grenzo by paying 2, putting Sling-Gang Lieutenant onto the battlefield.
Activate Sling-Gang Lieutenant's ability by sacrificing a Goblin, causing an opponent to lose one life and you to gain one life.
*Use Priest of Gix for the random card if available and place on bottom of stack*
Insidious Dreams Piles
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Many of the piles for Insidious Dreams are essentially the same for Doomsday, with an additional card to put the rest on the bottom of your library.
Most of the piles require you to draw a card, so the better moment to cast Insidious Dreams is right before starting your turn.
Unfortunately, you won't have slots available for mana acceleration, so the focus here is more on the cards you have to discard to pay for Insidious Dreams' additional cost.
Grenzo - Howltooth Hollow/Spinerock Knoll/Temple of Malice - Maralen of the Mornsong
This pile only requires 2 cards and 3R mana to go off. Therefore, it's the one I recommend in most cases.
- draw the land and play it.
- put Maralen of the Mornsong on the bottom of your library.
- at the end step before starting your turn, flip Maralen.
- on your draw step, tutor for Stranglehold and cast it to lock the board.
Grenzo - Howltooth Hollow/Spinerock Knoll - Murderous Redcap - Skirk Prospector - Metallic Mimic - Random Card
This combo requires 5 mana to go off.
- play Insidious Dreams stacking the cards above
- draw the hideaway land and play it, exile the 4th random card
- put Redcap, Prospector and Mimic in order on the bottom of library
- flip cards with Grenzo, sacrifice Redcap to help with mana to flip Mimic (keep trigger on stack)