The role of a Med Kit Scrapper in both large and small scale fights is to support your allies, similar to other supportive roles such as the Firebrand. As such, your focus in the fights need to be on your allies rather than your enemies. That being said, don't forget where the enemy are or what they're doing, just focus more on helping your allies. Some of the support provided by the Scrapper is, similar to the Firebrand, cone-based. What this means is that certain skills affect targets in a cone in front of you, rather than in a big area around you. Notably, Med Kit #1, #2 and Elixir Gun #3 are of this type.
One way to look at the purpose of a Scrapper is to look at what it uniquely offers to the group. Simplifying it, there are three aspects that Scrapper does well and makes it worthwhile to have in a group.
1) Consistently high healing per second
2) High amount of condition cleanses (thus a lot of boon application due to the Purity of Purpose trait)
3) Great access to Superspeed
When playing, your goal is to maximize these three aspects in all ways possible. A key trait in the build is that the Purity of Purpose trait which makes each condition cleanse you provide, to yourself or an ally, convert that condition into its corresponding boon (https://wiki.guildwars2.com/wiki/Condition#Condition_conversion for a handy guide). Regarding the first aspect, your Med Kit provides great sustained healing for your allies with just the auto attack (#1). Just #1 doesn't allow your allies to sustain through a spike however, so make sure to weave in bursts of healing available through #2, #4 and the toolbelt skill (F1) between your #1 spam when necessary. It's worth noting that both the Med Kit #1 and #2 only apply to allies and not yourself.
The key to utilizing the Med Kit properly is to realize what each ability actually does and what your other options are to tackle any given situation. For example, Med Kit #3 is an AoE field that is put at your feet and pulses a few times cleansing conditions each pulse. Elixir Gun #3 also cleanses conditions, but it does so in a cone in front of you and cleanses one condition per pulse for five pulses. The important difference between these two skills, AoE type aside (cone vs field), is that Elixir Gun #3 doesn't apply to yourself. When your allies need condi cleanses but you don't, it's better to use the Elixir Gun #3 and save Med Kit #3 for when you need those cleanses yourself. If a specific person needs a burst of healing, it may not be necessary to use Med Kit #4 (unless you're low yourself), rather aim your Med Kit #2 towards them (an ally can be hit by multiple bandages, so the closer you are to the person the more you can heal them with #2). Similarly, if you only need to cleanse a couple of conditions for your allies and they also need healing, throwing out Elixir Gun #5 and possibly using F1 next to them, gives them the cleansing they need without wasting the better condi cleanses available through Elixir Gun #3 or Med Kit #3. Finally, to be a pro with the Med Kit you need to spam #1 as soon as you're not doing anything else more important.
In short, condition cleanses are to be utilized in the following way:
Conditions on yourself and allies: Med Kit #3
Conditions on allies: Elixir Gun #3
Low number of conditions on yourself and/or allies: Elixir Gun #5
The third aspect of the Med Kit Scrapper is the regular Superspeed application it provides. By blasting fields with medkit 5 or elixir gun 4 you apply superspeed to allies. Do note that by performing leap finishers with your hammer 3 you only apply superspeed to yourself, so blasting is still the way to go for aoe superspeed. The changes that are noteworthy with this is that it no longer is limited to lightning fields, so you can blast any field for the superspeed. This gives you more help in applying it.
Your gyros give aoe superspeed upon the final pulse. So make sure to not overlap gyros as superspeed does not stack. For optimal use of superspeed with the gyro rotation you will have to pop the gyros after eachother in a proper rotation, so that your cooldowns on them will be done and that you then can keep the sustain up with the gyros. Your stealth gyro, while it helps with stealthing allies who might need help, also gives superspeed on final pulse. Do not be afraid to pop it in the rotation. Do note that if your commander is prone to use stealth gyro for engages when veil is not present then you should keep it saved pre-engage and only start using it freely in your rotation after the engage. (Do ask the commander how he prefers the stealth gyro to be used or if you have free reigns in using it whenever.)
Your function gyro gives aoe superspeed upon casting, do pay attention to if the commander calls for this upon engage or not. Otherwise you take your own initiative to use it. Just make sure to not use it too early when out of combat, otherwise you waste the superspeed. (Out of combat superspeed is capped at 40% movement speed increase vs 100% movement speed increase in combat.)"
Med-Kit aside, there are a lot of useful skills that haven't been discussed yet. In this section the notable skills will be listed along with typical use-cases.
You shouldn't be in hammer for 99 % of the fights, but there are still great uses for it. Firstly, Thunderclap (#5) should be used to stun enemy targets that have no stability to help the group kill them. The most typical situation is when a warrior of ours puts down a bubble stripping the boons of all enemies inside it.
Skills #2, #3 and #4 on hammer are all situational and can be used to save yourself or others in various ways. #2 reflects projectiles and can be used while you're trying to get out of danger or to body block for an ally being targeted by projectiles. Same goes for #4, which instead of reflecting projectiles, blocks attacks for 2 seconds. The leap (#3) can be used to get away from enemies while in combat.
The #1 and #2 on Elixir Gun are fairly useless and #3 and #5 have already been discussed. However, #4 is a great positioning tool to master. It's a 550 range backwards leap, as well as a blast finisher. To best utilize this skill, you should bind "About Face" in the control options to an easily accessible key. It allows you to quickly move out of danger or to reach an ally in need quicker.
Remember that all Gyros apply superspeed at the final pulse.
There are two ways to start your gyro rotation and it depends on what party you are in.
- Bulwark Gyro: If you are in a commander group -> Start off with Bulwark Gyro to absorb as much damage from, not only your party but essentially your commander, as possible to ensure that he/she survives the engage. Do however look out for if the commander party has scourges in it. They will most likely pop their party barrier so you might be able to use Purge Gyro instead to not waste Bulwark. If no scourges, then pop Bulwark.
- Purge Gyro: If you are in another party which most likely has scourges -> Start with Purge Gyro to ensure that your casters do not get any movement impairing conditions that could potentially lag them behind in the push. Important to cleanse them early on in the engage to make sure that they are receiving as little condition pressure as possible. The scourges also have party barrier that they should be popping, so using bulwark instead at first can be wasteful. Good to know that the Purge Gyro pulses 5 times, meaning the condition removal goes in pulses over 5 seconds and is not a one time cleanse burst. It is also a light field that moves with you so you can whirl it for additional condition conversion in general.
Once you have popped either of the gyros you then continue the rotation by popping the next gyro if still in fight to ensure a continuous superspeed upkeep since they have a fairly low cooldown of 20 seconds (excluding the uptime of each popped gyro). Do make sure to not overlap Gyros, as superspeed time does not increase like swiftness would if you apply it over each other. It simply replaces the older superspeed, causing you to lose out on the previous leftover superspeed. You want to chain your Gyros, just like how warriors can chain their bubbles (Winds) after each other when spiking.
- Stealth Gyro: Do note that if the commander does not actively call for your Stealth Gyro then you are free to use it at your own initiative during fights to stealth targeted allies who might be receiving too much pressure, causing enemies to lose their target. And superspeed at last pulse!
If you can keep the Gyro rotation steady then you can have a very high upkeep of superspeed, not even mentioning the blasts you can do in ANY field for additional superspeed and the function gyro superspeed upon cast.
The Supply Crate is quite bad as a skill due to its long cooldown and low damage (due to your minstrel gear). The only use for it is for a long stun on targets without stability. As such, the key moment to use it is in a good warrior bubble.
- Bandage Self is a big heal, both for personal and supportive use. Remember that the cooldown on this resets if you hit 25 % health.
- Healing Mist is a personal stun break. Save this for when you really need it, it's your only reliable stun break.
- Chemical Field applies a poison area that pulses 4 times. (33% less healing effectiveness) This is optimal to use on downed enemies that you pass to apply additional pressure and to make it less likely for them to get revived by firebrands who decide to MI to them.
- Detection Pulse: 5 targest reveal on a 900 radius, good for revealing enemies who veil nearby to reduce the stealth advantage enemies have on engaging your group. It also removes aegis, which is good for engages too so that other attacks can hit the enemies. Recommended to use it more often during fights after the first engage, off cooldown. This to keep their aegis popped off as often as you can.
- Function Gyro provides not only an aoe revive/stomp but its main selling point in zerg fights is the access to instant aoe superspeed upon casting. Use this as mentioned in the text above.
As a final note, the Function Gyro (f5) can both help you out a ton in battle and have virtually no impact, depending on how you make use of the skill. Stomping isn't really a thing in most large-scale fights so avoid summoning it on downed enemies as it'll then be on cooldown. However, if you summon it on allies who are downed and need to be ressed you will speed up the ressing considerably. This is only if you really MUST help with reviving someone, such as the commander, if MIs are slow or other helpers are slow. Scrappers essentially should not be trying to revive allies as it is not their main job. Ideally, the function gyro should be used for the superspeed (proactively) in fights and engages to avoid spikes along with other sources of superspeed.