Just Because you've beaten the Major 4 and become a master does not mean that you have access to every monster in the game. Many of them have story-based quests involved with unlocking the type. Some of these quests will then give you one of that type monster. (Zilla, Undine, Wracky, Mock, Durahan, Centaur, Joker, Bajarl, Ghost, Beaclon, Jill, Metalner, Phoenix, and Ducken) If you sell or use these monsters, you cannot get another within the game, you must get them off a CD. (With the exception of Dragon, Durahan and Ducken, which you can keep creating.)
Niton is unlocked at the same time as Undine, but is only available off CDs, it cannot be made in-game through any item.
Monsters unlocked with the stable upgrade, Baku & Golem, must be gotten off CD, they are not made in-game with any item.
The monsters unlocked by the elimination tourney (Gali, Henger, Mew, Worm) must be gotten off CD, they are not made in-game with any item.
The monsters available from the beginning of the game must be gotten from CD, except for the seasonal types available in the Market. See the FAQ thread on Market Monsters for more details.
Some sub-breeds are locked others are not, regardless of the status of the main type. Sub-breeds of monsters available from the beginning of the game are also available right away. The sub-breeds which have locked main types, that are available from the beginning are Worm, Gali, Golem, Dragon, and Baku. All other sub-breeds will be unlocked as their main breed is unlocked.
1. Ape- Available at the beginning of the game.
2. Arrowhead- Available at the beginning of the game. Available in Summer in the Market.
3. Baku- Get your first stable upgrade at 4th rank, in the 4th week of May. You should be able to get Bakus off of CD's at the shrine.
4. Bajarl- Must be 8th rank (beaten 2 of the big 4). Get the last house upgrade on the fourth week of May. You will be given the Bajarl pot by Binto. Use in combining to get the Bajarl.
5. Beaclon- 1. Must raise any breed of worm to four years old by the 4th week of June. 2. Must feed at least 30 cup jellies. 3. Have no stress and be very well on the fourth week of June when expected to cocoon. 4. Must have 80 loyalty. The Beaclon will then finish out whatever was left of the Worm's lifespan, but you can use it in combining later to have a Beaclon baby to raise.
P.S. The beaclon is one of the most controversial monsters to get. From my experience, I got a C class, worm/plant that was born on the 1st week of June to cocoon by following these guidlines. Some people have better luck with a D class worm. Freezing does not affect the result. Tecmo's website states that obtaining a Beaclon has a random element. Sometimes you can do everything right and just not get a Beaclon!
6. Centaur- Be 4th rank or above. Have a B class monster go to the power errantry during the months of March through August. It will randomly find a spear. When your monster gets back to the ranch, he will be attacked by a centaur. Your monster doesn't need to win but will be given a spear. Use the spear in combining to get a Centaur.
7. Colorpandora- Available at the beginning of the game.
8. Dragon- Be 6th breeder rank or higher. Have a B class monster be invited to the 2nd. week of Aug. Dragon tusk tournament. Beat the dragon and recieve the tusk. Use in combining to get a dragon. This event can be entered over and over (as long as a monster is at B rank and on the ranch to receive the invite) to get multiple tusks.
P.S. The dragon you fight in this tournament is extremely strong for a B class monster. Be prepared.
9. Ducken- Collect 5 diamonds from the cup jelly lids. Send away for a ducken doll which you will sell or give to your monster. After this, go to the Torles mountain expedition with Roveest. Find the strong glue, it is randomly placed in one of the 3 trees near the front. (Finding the glue can be difficult. Its appearance seems to be random. You may have to reset your game, or return several times to find it!) Collect five more diamond marks and build another ducken doll with the strong glue. Use this in combining to get the ducken.
P.S. You can get as many duck dolls as you want before and after getting the strong glue. You can never get rid of the strong glue after you find it unless you use a gameshark.
10. Durahan- Find the old sheath at the Parepare expedition, usually in the building beside the tusk tower in the middle of the map. Talk to the item lady about the stolen swords. Have an A class monster, it MUST be A class, to get invited to the Double Edged tournament the 4th week of February. The invite arrives in week 1 of February. Win the double edge and use in combining to get a Durahan. You can enter this event over and over to get multiple swords.
11. Gaboo- Available at the beginning of the game. Available in Winter in the Market.
12. Gali- Compete in the Elimination Tournament (NOT an elimination type tournament, It will be titled Elimination) on the 4th week of June after you get your monster to D class. Win this tournament and you will be invited to the IMA vs. Fimba Tournament. You do not need to win. The tournament happens every four years after that as long as you have a monster D class or above. You will only get a written invite the first time, after that it only shows up in the battle calender. You may fight in any rank above D. You will now be able to get Gali off of disks in the shrine.
13. Ghost- Let a monster die. Build a shrine for it. About every 140 weeks you will be asked to upgrade your shrine. Upgrade it twice. After that you will get in trouble for not taking care of it. Colt will clean the shrine and find a stick. Use the stick in combining to get a ghost. You will not see any other storyline events regarding the shrine, except a picture of it during funerals.
14. Golem- Get your first stable upgrade at 4th rank. It will cost approximately 15,000. You will now be able to get Golems of CD's in the shrine.
15. Hare- Available at the beginning of the game. Available in Fall in the Market.
16. Henger- Compete in IMA vs. FIMBA. See gali requirements for more details.
17. Hopper- Available at beginning of the game.
18. Jill- Be 6th rank or higher. Find the big footprint at the Torles mountain expedition. It is in the snowman shaped building in the upper right hand corner of the map. Send a B class or higher monster to the speed errantry. You should get a warning for Bighands, the first time you go. You will not get the warning again, but do not be discouraged. You can sell the Footprint now, as it will not affect your chances of encountering Bighands. You will randomly fight Bighands, a very powerful Jill. Beat him and you will recieve the Big Boots. Use these in combining to get a jill. You will only ever get one set of boots so use them wisely.
19. Jell- Available at the beginning of the game.
20. Joker- Be 4th rank or higher. Find the Joker mask at the burnt alter in the Kawrea expedition (your monster must be at B rank to be invited). Use the mask in combining to get a joker. The Joker Mask is one of the most difficult to find items in the game. It may take several trips to find it! Be Patient! For many ranchers it has taken 40-50 tries.
Tecmo's website says you must find the Phoenix Feather before being allowed to get the mask. This is not true, several people have found the mask first.
21. Kato- Available at the beginning of the game.
22. Metalner- Be 8th rank or higher, and get the second stable upgrade. In a clear September you will be visited by aliens three times. On the third week, they will give you a crystal. Use the crystal in the shrine. You will now be able to get metalners off of CD's in the shrine.
23. Mew- Compete in the IMA vs. FIMBA battle. For more detail, check the gali information.
24. Mocchi- available at the beginning of the game. Always available at the Market.
25. Mock- Be 4th rank. Visit the item lady until she gives you the mysterious seeds. While at rank 4, the mock seeds will replace a new item which would have appeared for you at the items shop. You must visit during a non-sale week. Colt will plant the seeds and about 10 years later the tree will die. Colt will ask if you want to water it, say yes. After this, let a monster die and the mock will appear in the stable.
New items appear in the item shop every 140 weeks, based on your first visit to the shop. There are a limited number of these items. You need to be at 4th rank, before Manseitan becomes available, or you will never get the seeds.
26. Monol- Available at the beginning of the game.
27. Naga- Available at the beginning of the game.
28. Niton- Be 4th breeder rank or higher. Raise a hopper of any breed to B class. The hopper will dig up the hot springs in winter: Dec., Jan. or Feb. You will then recieve the undine slate. Use the slate in combining to get an undine. You will now be able to get nitons off of CD's in the shrine. There is no more storyline about the hotsprings in the game.
29. Phoenix- Find the Fire feather at the Kawrea expedition. You can find multiple feathers. Use feather in combining to get the phoenix.
30. Pixie- Available at the beginning of the game.
31. Plant- Available at the beginning of the game.
32. Suezo- Available at the beginning of the game. Available in Spring at the Market.
33. Tiger- Available at the beginning of the game.
34. Undine- See niton requirements.
35. Worm- Compete in the IMA vs. FIMBA tournament. For more details, see the Gali requirements.
36. Wracky- Be 7th rank with high Fame. You will recieve a scary doll in the mail. Keep the doll when Colt asks if you want to throw it away. Let a monster die and the wracky will appear in your stable.
37. Zilla- Complete all the requirements for Niton. Be 6th rank with a B class or higher monster. Send a monster to the skill errantry and you will hear a warning for a large water monster. You will hear the warning just once, but from then on you have a chance of facing the monster. You will randomly fight the Zilla King. Beat him and you will recieve the Zilla Beard. Use in combining to get a zilla. You can only get one Beard in the game, so use it wisely.
38. Zuum- Available at the beginning of the game. Always available at the Market.
The original thread was written by Vheod, I am just adding in the corrections that I could find. -Miss Carrie Additional info by Quincunx, Shaoran, kgrind, Blackish_, Gamelegend3, and Dark Phoenix.