Because SNK doesn't want to nerf this annoying unit, I'd just like to share some of my experiences. If you do not have an answer to this unit, you will be utterly destroyed on the short maps, especially if the opponent also packs Iori/Slug Armor (and everyone who is not me has Slug Armor). Note that if it's 2v2, you can still be screwed over if you get a lousy partner and you are up against Green Hazmat + Iori/Slug Armor/Mai on a short map.
Both Green Hazmat and Mummy have 2000 HP. Note that the rolling mummy ball from the Green Hazmat does a ton of damage (maybe 1.3k+?), which is actually the main reason why it can be difficult to counter when spammed. The grenade also does the same damage (wtf SNK). The balls can roll under Smasher and spawn the mummy behind it, which will 'lock' Smasher in position and make it attack air.
Hard counters:
- Red Ring Laser Mecha: Let it use its standard attack, NOT the special attack. Two rings will wipe all the spam clean. As a bonus, it rips into the Green Hazmat + Snail House combo. However, you leave yourself wide open to Slug Armor (which beats 99% of all units under 350AP). If you're backed up against your base when this happens, you'd better pray you have a melee unit to kill Slug Armor or to at least stall until you MSA it. If not, Red Tar Man or Augen PM are your friends. If using the former and you're really pinned, let Slug Armor attack once BEFORE you send out Red Tar Man to avoid the laggy knockback. In 2v2 it loses some effectiveness because people will pair the hazmats with annoying units like Robert, King or Leona (Leona's special up close can cancel rings), so you may need help from your partner.
- Slug Armor: what did you expect lol slug armor is emperor of the early game. Still, it will eat a lot of damage while clearing, so you may want to look elsewhere, or check out some of these other units to support it.
- Yuri: She was born to counter Green Hazmat. Avoids balls with her special and OHKOs. Her normal is also good at killing mummies and soldiers. I don't use her but it seems like you'd need some skill to aim her special. There is still a chance a mummy will end up behind her so have backup units ready.
Soft counters:
- Ring Laser Mecha: Solid if you're a good distance away, but if the map is short, you may end up with a mummy in its face, which will mess up the targeting of the special. Balls kill it quickly.
- Rebel Zombie: The special can fly past a rolling ball and OHKO the Green Hazmat behind it. Note that a good opponent will throw the ball early to avoid this, forcing the Rebel Zombie to use his normal attack if the map is too short, but you can at least kill the mummy by summoning another zombie, and you won't ap feed. It is important to send it immediately or the special won't charge quickly enough for it to be a threat. If the special charged faster, it would be a hard counter.
- POW motorcycle: Guaranteed knockback, kills in two hits. Useless lategame, and quite easy to kill. At least Green Hazmat is useless lategame, too.
- Mini UFO: Two zaps will kill. Obviously not meant to be used alone (it needs to follow a grounded unit to advance), but has surprising synergy with other units, and as a bonus it will help chip away at Slug Armor. I used to run an Alien deck (before Gigants) and the combination of Rebel Zombie + Mini UFO shut down Hazmat openings with surprising ease. Lategame presence is questionable however, with all the AOEs out. Pairing it with Smasher gives mixed results since if you're really unlucky, it will dip, eat a mummyball, and then get killed by the mummy's breath. Works brilliantly with any other wall (e.g. Armor Unit + Mini UFO).
- Mini Hermit: Bulldozer. Unfortunately, almost anything else (especially Slug Armor) turns it into an AP feed, and the Green Hazmat's attacks wear it down severely.
- Smasher: OHKOs, but prone to baiting and getting trapped by rollunder balls.
Misc: Mini-list of early game units that ONE-SHOT a Green Hazmat/Mummy.
- Rebel Zombie (special only)
- Hopper Mecha (both normal and special, not recommended though since if a ball hits it it sometimes explodes before the mummy can be damaged)
- Special Forces Rider (have never tried him. Expensive to summon though considering you just kill one mummy/hazmat, and special charge time is crappy. The special is definitely an OHKO, not sure about the normal.)
- Smasher (vulnerable to balls rolling under it and forcing it to attack air.
- Mini Hermit (may AP feed because the balls just do too much damage)
- Red Tar Man (beware its nonexistent knockback resistance, and make sure it doesn't get hit by a ball before it throws vomit. The vomit is also hard to aim at long range. However, if a mummy is right in front of the base, it will eat all vomits and die. There are better options.)
- Tiny UFO Type: A: Technically deserves to be here as one full volley (5 shots) will kill a Mummy/Hazmat (it does no knockback). Not the best option as it may end up spreading out its bullets between summoned mummies, wasting time.
- Mai (special)
- Iori (special)
- Yuri (special)
Additional notes:
- Sometimes it's worth it to let the base take some damage rather than to send out fragile units to die to the balls and feed AP.
- Zombie Eri and Clone Fio do NOT oneshot Green Hazmat, don't even try using them as a counter at the start of a match. They are massive AP feeds. Not even Zombie Fio/Marco OHKO them.
- Multihitters such as Armor Unit and Trevor are also bad choices as they'll just knock the Green Hazmats back.
- Mutated Soldier does not work, the special simply doesn't charge fast enough, and it gets OHKO'd by the balls.
- Nadia is NOT a counter, her cocktail's damage is just too low.
- Hunter Walker is a very questionable counter, it may or may not align with the targets.
- Red Samurai Infantry is somewhat useful for stalling and will probably kill one mummy. Don't spam him, just use him to stall until you can send out Red Ring Laser Mecha.
- The mummyballs did no damage in the original Metal Slug 4. wtf are u doin snk
Things I have not tried:
Special Forces Rider
R. Shobu ver PM
Other KOFs (I refuse to use them, but if you know of any I'll add them.)
Orange Hazmat (I doubt it...)
Clark