
However, the ability text of the original does get copied, so the first ability, whose effect is applied after the copy effect, will count the number of creatures currently in the graveyard, and put that many +1/+1 counters on the clone. If you copy the troll with Clone-like creatures, the number of counters on the original troll doesn’t matter - counters aren’t copiable values. The effect replaces the Troll’s entering the battlefield, so it functions before the troll hits the battlefield, and in this case the troll card is still in the graveyard at that time, so it counts. If an effect puts Golgari Grave-Troll onto the battlefield from the graveyard, the Troll’s first ability effect will take it to consideration as well. It doesn’t matter through what means the Troll hits the battlefield: you can cast it, or just put in onto the battlefield from your hand or from any other zone through a related effect (such as Show and Tell). This ability is static, so it cannot be countered. Golgari Grave-Troll’s first ability is a static one and generates a replacement effect: Golgari Grave-Troll enters the battlefield not as is, but with a +1/+1 counter per creature card in its controller’s (indicated by the word “your”) graveyard. In all zones except the battlefield, the Troll’s power and toughness are always equal to the printed values - 0/0. If you control Golgari Grave-Troll, Thrun, the Last Troll and Skeletal Vampire, then through Coat of Arms’s static ability Golgari Grave-Troll gains +2/+2, and the remaining two gain +1/+1.

As such, while on the battlefield, it will gain a bonus off Death Baron’s static effect, and it will be a legal target for Undead Slayer’s activated ability. Golgari Grave-Troll is a green creature with two subtypes: Skeleton and Troll.
