Here's an example of what the tail slash may look like.
[ATTACK:SCYTHE:BODYPART:BY_TOKEN:TAILSCYTHE]
[ATTACK_SKILL:STANCE_STRIKE]
[ATTACK_VERB:slash:slashes]
[ATTACK_CONTACT_PERC:100]
[ATTACK_PENETRATION_PERC:100]
[ATTACK_FLAG_EDGE]
[ATTACK_FLAG_WITH]
[ATTACK_PRIORITY:MAIN]
Before I jump into any explanations, I'm going to leave these wiki links on attack tokens and syndromes, since they may be able to help a bit.
http://dwarffortresswiki.org/index.php/DF2012:Creature_token#Attack_Tokenshttp://dwarffortresswiki.org/index.php/DF2012:Syndrome#Creature_effect_tokensFor examples of venoms, try looking up some of the various snakes on the wiki. I'm not quite sure what you want to do with it, but there are a lot of different effects you can do.
[ATTACK:SCYTHE:BODYPART:BY_TOKEN:TAILSCYTHE]
The first argument is an ID that you get to decide. After that you put whether it is a standard body part or a child bodypart/tissue layer. The child part is only really for scratching with a specific tissue or selecting smaller parts such as teeth. It's a bit like body plans, where you choose the body part you want to use for the attack using BY_CATEGORY, BY_TOKEN, or BY_TYPE
[ATTACK_SKILL:STANCE_STRIKE] This is just for what type of skill the attack uses.
And here is a list of skills in the game.[ATTACK_VERB:slash:slashes] The verb is what the combat log displays when the attack is used. The first verb is the first person message (You slash the swordsman), and the second is the third person message (The kizaur slashes the swordsman).
You can also use [ATTACK_FLAG_WITH] to make the combat log tell you which body part used the attack. For example, when the game points out that a dwarf punched with their left hand instead of their right hand.
[ATTACK_FLAG_EDGE] Makes the attack an edged attack, otherwise it is a blunt attack.
[ATTACK_PRIORITY] can be either MAIN, or SECOND, which affects the likelihood of the creature using the attack when controlled by the AI.
[ATTACK_FLAG_CANLATCH] Means that the attack can catch an enemy, like what happens when a creature bites. Latched attacks can then shake around to deal more damage. You may want to use this tag for your blood sucking and venom injecting attacks.
To make an attack suck blood, you give the attack [SPECIALATTACK_SUCK_BLOOD:#:#] where the numbers are the minimum and maximum amount of blood that will be drained during an attack. You will have to break a tissue layer in order to successfully suck blood.
[SPECIALATTACK_INJECT_EXTRACT] Allows you to inject a material into the enemy. Like sucking blood, the attack will have to penetrate the opponent. The material will have to be defined like other materials. I.e: [SPECIALATTACK_INJECT_EXTRACT:LOCAL_CREATURE_MAT:VENOM:LIQUID:100:100]. The arguments are a bit like tissue materials. You may want to directly define the venom within your creature's raws, since it is likely the only one using it. The injected material can be either SOLID, LIQUID, or GAS, and you specify the minimum and maximum amount injected into the enemy. You will have to learn how syndromes work to give your material an effect.