Hardened Scales can affect Walking Ballista's first ability (so that Walking Ballista will enter the battlefield under your control with X plus one +1/+1 counters on it, provided X is greater than 0) (C.R. 122.6). Hardened Scales also affects the number of +1/+1 counters put on a "creature you control" when an effect such as graft "move(s)" a +1/+1 counter onto that creature (C.R. 122.5, 702.57a). See also this thread.
In general, a counter is "put" on a permanent if the effect says "put ... counter[s]", "move ... counter[s]" (C.R. 122.5), or "enter[s]" or "put ... onto" or "return ... to" "the battlefield ... with ... counter[s]" (C.R. 122.6). See also this thread.
EDIT (Mar. 9, 2020): Some rules were renumbered with Core Set 2020.
Assuming X is 1 for Walking Ballista, Walking Ballista will enter with two +1/+1 counters on it, rather than one (thus, it will enter as a 2/2 creature, not 4/4 [C.R. 613.1g, 613.3d, 613.4, 603.6b]). This will make Llanowar Reborn's graft ability trigger if Llanowar Reborn has a +1/+1 counter on it, and when it resolves (and Llanowar Reborn has a +1/+1 counter on it), you may move a +1/+1 counter from Llanowar Reborn onto Walking Ballista (C.R. 702.57a). If you do, Walking Ballista will be given two +1/+1 counters this way instead of one (due to Hardened Scales), so that in the end, Walking Ballista will have four +1/+1 counters on it.
What with multiple instance of graft? Does each instance give an additionnal counter or it doesnt matter how many creatures grafts and you always get one additionnal counter?
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What with multiple instance of graft? Does each instance give an additionnal counter or it doesnt matter how many creatures grafts and you always get one additionnal counter?
The grafts will add two counters each.
Each instance of Graft triggers on its own when the creature enters. Their controller puts them on the stack in any order they want. They will resolve one at time. As each one resolves, Scales applies and makes it add two counters rather than one.
I am sorry, I want to comment on the case: a walking ballista of its X = 1 enters the battlefield when one Hardened scale is on her controller’s battlefield.
Any creature itself if at any moment became a 0/0 creature, it should be destoryed (destory being triggered more accurately) the wording ‘with X counters on CARDNAME’ should never wait for any action of putting +1/+1 counters on it, instead the counters are already on the Walking ballista at the first moment it is on the battlefield.
Therefore, Hardened scale should not affect Walking ballista when the WB resolves.
I do not think ‘X/X creatures with a/b counter on it’ is a triggered ability, unless the wording is changed to be like ‘CARDNAME is a 1/1 creature, when CARDNAME enters the battlefield, put X +1/+1 counters on CARDNAME’ in the second case it is a triggered ability, but not the current ones.
For the purposes of Hardened Scales, a counter is "put" on a creature, among other ways—
by giving a creature that counter as it enters the battlefield (including by an ability of the form "[This creature] enters the battlefield with ... counter[s]", such as found in Walking Ballista) (C.R. 122.6), and
by "mov[ing]" a counter from another object onto that creature (C.R. 122.5).
Thus, in this scenario:
If X is 0, Walking Ballista would not enter the battlefield with any +1/+1 counters on it; since no +1/+1 counters would be put on Walking Ballista here, Hardened Scales would not add another (C.R. 614.7). However, Llanowar Reborn's graft ability will still trigger (since another creature just entered the battlefield) if Llanowar Reborn has a +1/+1 counter on it (C.R. 702.57a), but graft won't do anything right away (C.R. 603.2) and Walking Ballista will then go to the graveyard (not: be destroyed) as a state-based action for having toughness 0 or less (C.R. 117.3b, 117.5, 704.5f). As a result, Walking Ballista won't be there to move a +1/+1 counter to by the time the graft ability resolves (review C.R. 702.57a).
If X is 1 or greater, Walking Ballista would enter the battlefield with X +1/+1 counters on it, but Hardened Scales adds one more, so that Walking Ballista enters the battlefield with X plus one +1/+1 counters on it instead. Also, Llanowar Reborn's graft ability will trigger if Llanowar Reborn has a +1/+1 counter on it, but the ability won't do anything right away (C.R. 603.2, 603.4).
It is correct that an ability of the form "[This creature] enters the battlefield with ... counter(s)" is not a triggered ability (it doesn't begin with "when", "at", or "whenever") (C.R. 603.1). Rather, it's a static ability with a replacement effect (C.R. 604.1, 614.1c), and that effect works immediately (C.R. 614.6).
On the other hand, an ability of the form "Whenever another creature enters the battlefield, ...", such as found in graft, is a triggered ability, since it starts with "Whenever" (C.R. 603.1, 702.57a). Like any other triggered ability, it has no effect unless and until it resolves (C.R. 608.2, especially C.R. 608.2c; C.R. 609.1).
Therefore, Hardened scale should not affect Walking ballista when the WB resolves.
Incorrect. Assuming X is anything bigger than zero, Hardened Scales does interact with Walking Ballista: Ballista enters the field with its own counters AND with those given by Scales. (rule 122.6)
I play a llanowar reborn into a walking ballista
Ballista enters as a 2/2 and then I move the graft counter onto it making it a 4/4.
Is this correct?
In general, a counter is "put" on a permanent if the effect says "put ... counter[s]", "move ... counter[s]" (C.R. 122.5), or "enter[s]" or "put ... onto" or "return ... to" "the battlefield ... with ... counter[s]" (C.R. 122.6). See also this thread.
EDIT (Mar. 9, 2020): Some rules were renumbered with Core Set 2020.
EDIT (Mar. 9, 2020): Correctness edit.
Because of the delay, an opponent could kill it with Shock.
RULES OF MAGIC :
http://magic.wizards.com/en/game-info/gameplay/rules-and-formats/rules
It sees a 2/2, because the Ballista entered as a 2/2. It only becomes a 4/4 later.
Graft is a triggered ability that uses the stack. It only adds its counter after the creature had already entered the battlefield.
The grafts will add two counters each.
Each instance of Graft triggers on its own when the creature enters. Their controller puts them on the stack in any order they want. They will resolve one at time. As each one resolves, Scales applies and makes it add two counters rather than one.
Any creature itself if at any moment became a 0/0 creature, it should be destoryed (destory being triggered more accurately) the wording ‘with X counters on CARDNAME’ should never wait for any action of putting +1/+1 counters on it, instead the counters are already on the Walking ballista at the first moment it is on the battlefield.
Therefore, Hardened scale should not affect Walking ballista when the WB resolves.
I do not think ‘X/X creatures with a/b counter on it’ is a triggered ability, unless the wording is changed to be like ‘CARDNAME is a 1/1 creature, when CARDNAME enters the battlefield, put X +1/+1 counters on CARDNAME’ in the second case it is a triggered ability, but not the current ones.
Thus, in this scenario:
It is correct that an ability of the form "[This creature] enters the battlefield with ... counter(s)" is not a triggered ability (it doesn't begin with "when", "at", or "whenever") (C.R. 603.1). Rather, it's a static ability with a replacement effect (C.R. 604.1, 614.1c), and that effect works immediately (C.R. 614.6).
On the other hand, an ability of the form "Whenever another creature enters the battlefield, ...", such as found in graft, is a triggered ability, since it starts with "Whenever" (C.R. 603.1, 702.57a). Like any other triggered ability, it has no effect unless and until it resolves (C.R. 608.2, especially C.R. 608.2c; C.R. 609.1).
RULES OF MAGIC :
http://magic.wizards.com/en/game-info/gameplay/rules-and-formats/rules