This is a list of the "special" abilities of some of the creatures. If anything is missing or incorrectly plz let me know and ill add/correct it and post credits .
Desert Wyrm: About 1.2k each on the shard front, but if you use burrow to mine iron, in 15 iron (about 1 minute) you cover the cost. Burrow one while you mine the other 2, means extra iron
Spirit Tz-Kih: Right click players and he will drain prayer instead of damaging, quite handy for higher leveled duels and C Wars flag holders
Giant Chinchompa: Sometimes explodes from sheer excitement, and can range opponents. The scroll forces an explosion. The best time to use the scroll is when your Chinchomba is about to die anyways. Try to find monsters in groups that have low ish hp, like rock crabs
Compost Mound: Theoretically, he can earn a generous amount of farming exp for a starting farmer. Simply head to Catherby with your smelly friend and scrolls, and fill the bin, use buckets from Arhein on the bin, and refill after banking or storing in leprechaun. If you've unlocked it, you can buy super compost pots in Vinesweeper to get hundreds of super compost quickly, using familiar. Once you're done, kill your pet with buckets for some more compost. She (It's a mom) has a 25%? chance of making super compost with each special
Vampire Bat: Start of the strong attackers. Hits 12's fast and can heal himself. Also works as a light source. His scroll doesnt heal much, but it helps
Void Ravager: Can boost mining 1 on top of his invisible 1 boost. He also forages ores. Great mining pet but uses Green charms at lowish exp for the pouch. His scroll takes you to Pest Control lander
Void Spinner: Appears weak, but it heals you for 1 hp regularly, and the scroll can teleport you to the Pest Control lander. Having a pet healer is just great for thieving, fighting, anything using up hp
Void Shifter: For the safety minded individual, this pet is King. It teleports you to Pest Control if you drop below 10%, and the scroll can teleport you as well. Its combat is nothing to laugh at either. Use on new quests or areas you're not sure you'll survive in
Macaw: Obviously for use when hunting for herbs, from herb droppers such as chaos druids and chaos druid warriors. Using herbcall whenever special renews makes for fast exp indeed. Selling your potions should pay for the pet. Bird View lets you find the Giant Mole easily and quickly, or view C Wars for Flag hiders
Evil Turnip: One of the few methods of lowering an enemies ranged ability. Obviously, since Jagex loves rangers, this ability is a spell (which rangers are strong against), the seed is quite a rare drop and it grows only one turnip per seed. Could be used in duels if its unnerfed.
Pyrelord: Invisible 3 Firemake boost, and the scroll can smelt a piece of jewelry out of a gold bar. He can act as a tinderbox for 10 more xp per log than usual, tiny bit exp more for a bit of cost
Magpie: Free jewelry while you thieve, and booster to your abilities, a rogue's best friend. Best used in junction with Ardougne pickpocketing, so you can heal off cake and bank jewelry as needed
Bloated Leech: A quick way to heal disease and other ailments without expensive potions like Balm or Super Restore. Good for areas like Scabaras Hive, with that powerful plague but no nearby bank. Requires lots of food though
Spirit Terrorbird: Tireless Run ability allows you to run endlessly to far places, and it carries 12 items, so running for things like snapes are much easier, actually good for almost any situation
Ibis: Forages swordies while you fish on your own, giving lots of potential cooking exp, and paying for itself if you sell. The fishing bonus makes this guy a must have for those who love to fish. The Fish Rain scroll produces fish up to bass
Karamthulhu: The mage class summon that is the first step towards overpowered pets. You can right click him to feed summon points to it so it force casts a water spell that hits hard. Not only that, its doomsphere scroll allows it to hit a 16 max. Truly frightening potential for stakers =]
Spirit Graahk: Great Hunt boost, if the graahk has to move to get into combat, it will hit twice. Can teleport you to the Graahk area, and can be Goaded with scroll to hit enemies. Great for nature crafting when paired with duel rings
Spirit Kyatt: If you summon or call it into combat directly it will Pounce with a chance for triple damage. Boosts 5 Hunter invisibly, can teleport you to Piscatoris Hunt area (handy), and the scroll calls your pet for instant pain. Great for people trying to train quickly (teleport to near obelisk)
Spirit Larupia: Boosts 5 Hunter invisibly, can teleport you to Feldip Hills Hunt area, and the scroll uses a Magic attack to lower enemy Strength
Spirit Cobra: The ONLY way to get any Cockatrice other than the standard. You use its ability to convert any egg, including blue green and red god eggs, vulture, raven, and chicken into the respective cockatrice types, who all make unique cockatrice types. They SHOULD "forage" their own egg types, meaning you don't have to waste a new god egg etc to make more unless you didn't bother letting them forage or survive, but sadly they do not. Jagex should fix that, seriously
War Tortoise: This bad boy is the elite of Gold Charm use. He holds 18 items, making your inventory a whopping 46 spaces as long as he's up. He can fight too! If you plan on mixing fighting with item holding, be careful about what you fight, something too strong and it'll die. If you're up against a monster where you lose food at a fast rate, you may just want to let him fight till he dies/disappears, and pick up the food he drops. If you're getting a ton of loot, summon him near the end of the trip to free up 19 spaces (his 18 spaces and the 1 pouch space)
Bunyip: When fighting raw food droppers such as brine rats, waterfiends, or dagganoth. It's quite handy to be able to swallow whole those foods and not having to head back to the bank. Not only does he help you eat raws, But he heals you for 2 hp regularly! Also converts raw fish into water runes one at a time. Note: Heals 2 hp about every 12-15 seconds, healing you for 42 minutes, insane! If you wear a Regen Brace, pray heal hp, and even lunar sleep, you can heal VERY fast. Use a Unicorn instead for high sudden damage trips.
Fruit Bat: Planning on extended fighting in Karamja? This fella will continously supply food while he's with you there. He doesn't fight, so you needn't worry about him dying prematurely. He also can make pineapples (bring a knife), and watermelons.
Ravenous Locust: Another anti-player summon, it sometimes eats your opponents food, the scroll also eats their food, and as an added bonus it can remote view for you, helps with Mole or Clan Wars/ Fight Pits hiders
Arctic Bear: Counts as two pieces of arctic camo, meaning it's very helpful in catching anything in the cold north
Phoenix: Gives mage exp, hits quite often and fast, but has low defense and health. The ash attack makes the enemy miss more. The special lets it restore itself from the thrown ash attack, burning nearby enemies. Not good for hard hitting enemies, unless you have plenty of scrolls ready, and can special before it dies.
Granite Lobster: Possibly the best fishing to 99 beast there is? 4 invisible Fishing boost, and forages fish as you fish, you can get that 99 cooking much sooner than before
Praying Mantis: Truly frightening show of power by a summoner for pvp. It basically destroys your opponents ability to fight, in the long term. Unlike stunning, the drains stay all fight long unless they heal pray with pot. Also, the bind means if you range or mage (or halberd lol), you can get in extra attacks easily, and even more Mantis Strikes in
Forge Regent: Quite annoying for pvp fights, its special can unequip the target's weapon or shield
Giant Ent: In the essence mines, you can stay there and use it's Nature Link ability to get a large supply of nature and earth runes (which you can sell), as you mine the essence. Acorn Shot is great for low level farmers and helping damage crowds. Increases harvesting from cactus, belladonna and fruit trees!
Fire, Ice, Moss Titan: Basically all the same but train different stats. Their Scrolls all work like a half Sara Brew with no negatives. VERY good for boss fights
Hydra: Regrowth instantly regrows a Farming tree stump, letting you chop your favorite tree without any wait! Great for woodcutters, and more than pays for itself if you do Mage or Yews. Highly reccomended
Spirit Dagannoth: It has high stun rate with special if it hits, it makes it one of the most powerful summons there is. Most especially on things with low defense (team Spike Shot anyone?)
Lava Titan: Can hit 5 extra damage an attack, 10 invisible
Firemake and mining boost, can teleport you to the Wild's Lava Maze. His scroll sends a Magic attack that damages your opponents Special Bar. Favorite of Star Miners and penguin hunters needing a wilderness penguin
Unicorn Stallion: Cures ailments, heals you, and fights. The ultimate in defensive familiars. Great for places where major healing would be needed. Can heal 3 times in a row before special bar needs recharging, meaning a whopping 45% hp. Mainly used for monsters such as tormented demons or GWD bosses. 54 minutes of heavy healing, use a bunyip instead for low periodic damage trips
Geyser Titan: Ranges, can boost your range by 1+3% your level, you can use bowls on him to make hot bowls of water for cooking, you can recharge Glories on him!, and you can Use Boil to damage opponents based on their armor. So many uses for so little cost eh?
Wolpertinger: This is one frighteningly useful critter. He allows twice as many berries from berry patches, as well as
twice as much exp per berry, meaning 4 times experience per patch! He gives a hidden 5! hunter bonus, 5% bonus against
Magic, and his scroll allows him to mightily boost your Magic level! On top of this he fights, at a cool 210 Combat. He needs crimson charms for the pouch, but considering his usefulness we're lucky he's not blue charm
Abyssal Titan: Can store 7 Essences, and the scroll sends all pure essences in yours and his inventory to bank! Live in the Rune Essence mines forever!
Pack Yak: The best beast of burden there is, if only he could last longer and cheaper . This lovely beast can store 30! items, and not only that, his special ability allows him to bank a selected item in your pack, as long as its full. His expense is alleviated by the fact that, by the time you reach this level, his expense is chump change compared to what you'll be hauling back home in his loot sack (most likely dragon hides and bones), and you'll earn new crimson charms probably every run you go for
Steel Titan: Modestly named, this beasts scroll allows him to unleash 4 mighty ranged blows for his next attacks. On top of this, he invisibly boosts stab/slash/crush defence by 15%! This titan is almost impossible for players and monsters alike to kill, and makes you much harder to kill as well. A favorite of castle wars flag holders