what cards can double this effect.

[kal4444]

I was looking for cards to multiply the effect of putting bounty counters on creatures with Mathas, Fiend Seeker.  thanks

[Hozz101]

Vorinclex, Monstrous Raider (off color, I know)

Rings of Brighthearth

Lithoform Engine

Illusionist's Bracers

Battlemage's Bracers

Rowan Kenrith (On the Ult, so unlikely)

[CleanBelwas]

I think your best (maybe even your only) options are Lithoform Engine and Strionic Resonator.

Copying triggered abilities isn't a common thing, especially in Mardu, but these two will put in work and do what you want them to.

Unfortunately Hozz101, Mathas' ability is a triggered ability and not an activated one, so things like Rings of Brighthearth, Illusionist's Bracers and Battlemage's Bracers don't work with Mathas.

[Hozz101]

Hah, my bad. Thought it was a tap ability. I actually avoided saying strionic for that reason XD

[UrizenII]

It's a one-off, but Radiant Performer would do this in a brilliant way.  It has Flash, so you can cast it in response to Mathas's ability triggering, thereby putting a bounty counter on all creatures your opponents control (provided they are legal targets, of course).  Otherwise, I do believe Strionic Resonator and Lithoform Engine are the only cards in that color identity that can copy triggered abilities.

You might also consider making clones of Mathas.  Again, it's harder in Mardu (mostly a blue thing), but something like Helm of the Host would give you multiple copies of him, thereby giving you multiple triggers.  If you use Mirror Box or Mirror Gallery to get around the legend rule, there are a number of cards in red that can create token copies of creatures.  Unfortunately, the tokens they make typically go away at the end of combat (and therefor wouldn't trigger) or at the beginning of the next end step, in which case you'd only get one trigger off each copy.  It's not at all practical or advisable, but it would technically do what you want.

[Aetherium Slinky]

Proliferate + Nesting Grounds

No wait, there's no way to get the bounty counter on a creature you control. Sorry.

[Landale]

Proliferate + Nesting Grounds

No wait, there's no way to get the bounty counter on a creature you control. Sorry.

You could Enslave the creature you put it on, then do that.

[anjinsan]

Strictly speaking, putting bounty counters on the creature has no effect (at least, not as far as Mathas is concerned - having one or more counters would cause Chevill, Bane of Monsters to trigger, for example). The card draw thing is caused by the rest of Mathas' ability - it's an effect which is added to the target creature, and the bounty counter only matters in that the effect goes if there are no bounty counters left.

Thus, Vorinclex is pretty useless. The creature would get two bounty counters, but would still only get the card draw text once.

Likewise, Nesting Grounds is next to useless here, because putting a bounty counter on another creature doesn't add the text. This also applies to bounty counters provided by other effects, such as Chevill.

Conversely, if Mathas triggers twice he can give the effect to the same creature twice. That creature will get a second bounty counter, but it doesn't actually matter; one of them could be removed and it would make no difference, you'd still get two cards when it died.

As suggested, doubling Mathas' ability or getting clones of Mathas is really the only way to add that draw text more than once. Alternatively, you can make that effect happen more than once by doubling it (again, with cards like Lithoform Engine or Strionic Resonator) or with Teysa Karlov, since it's a death trigger.

[UrizenII]

Conversely, if Mathas triggers twice he can give the effect to the same creature twice. That creature will get a second bounty counter, but it doesn't actually matter; one of them could be removed and it would make no difference, you'd still get two cards when it died.

I completely missed that; the second portion of his ability text (the death trigger) specifies that as long as the creature has a (i.e. at least one) bounty counter on it, opponents draw one and gain two life when it dies.  It doesn't matter how many counters are on it, as the death trigger only occurs once.

That being said, duplicating the death trigger that actually draws cards is much more difficult because you don't actually control it; Mathas's ability specifically states that the creature with the bounty counter on it has the ability, "When this creature dies..."  Since the opponent's creature and not Mathas is the source of that trigger, you don't control it, so things like Teysa Karlov, Lithoform Engine, and Strionic Resonator would not copy it.  You can copy the end step trigger that puts bounty counters on things, but not the draw triggers.

Also, Chevill, Bane of Monsters or anything else that uses bounty counters does not work with Mathas.  Ruling on 08/25/2017: "Creatures that receive a bounty counter other than from Mathas’s ability resolving won’t gain the triggered ability. Creatures that receive more than one bounty counter as Mathas’s ability resolves (most likely due to Doubling Season) won’t have the ability multiple times."  The reverse is not true, however; Chevill's ability does not care where the bounty counters came from, so his ability would trigger off counters placed by Mathas.

[stuffnsuch]

A couple things to consider, there are a bunch of cards that make non-legendary copies of legendary creatures (though, admittedly not many outside of blue).  Once you have one non-legendary copy, any regular copy spells can copy the non-legendary copy.  Mirror Box and Co can also allow you to copy Mathas without the legend rule getting in the way.  Even "temporary" tokens (like the sacrifice at end of turn or end of combat sort) can be saved using End Turn effects.  Essentially, you could arrange to have a couple dozen copies of Mathas on the board with the right set up.  You can copy (more easily in those colors, as well) your Lithoform Engine or Strionic Resonator or just untap them to get more triggers, as well.  It's not an easy thing to pull off, but there are a few ways to make it happen.