Ok so I tested this out more and there's 2 points to consider.
1: The standard action buff at the begining of round. A lot of beatstick monsters don't have anything to do with that action, perhaps it could be said that if the monster can't buff, he should be able to give himself +5 on his next check (a sort of improved aid another).
2: Fast healing and regeneration: Do these things apply at each initiative or 1 round? I tend to lean towards each initiative because that makes it tougher and that's ok.
Having tested this more, I'd make the following modifications:
**SOLO MONSTER TEMPLATE**
+ 1 CR template.
automatically applies to any monster that fights alone vs a party of 3 or more.
**ALTERNATIVELY** In an event where a player fights alone vs 3 monsters or more he could benefit from it.
1) FASTER Roll 2 tracks of initiative, the highest is the full round in which the monster can perform, the lowest is a standard action and a swift action (no move, no full round). *MODIFICATION**: The lowest initiative cannot be immediately after the highest initiative, if a monster would act two times in a row, he must delay the second action until at least one PC has acted.
At CR 13+, the monster gains a third standard action that automatically starts at the beginning of the round, with the following caveat: The monster can use any 1 action that can target only the monster, even if it could normally affect other or multiple targets. Spells cast in this way ignore somatic components and do not provoke attacks of opportunity. The monster does not need to have a free hand to cast a spell in this way. The Monster is still considered flat footed for the purposes of the first round. The monster can also perform the self aid or healing surge action
At CR 20+, the monster has 2 initiatives, and 2 full round actions.
2)BETTER Solo monster can use their remaining movement at any time they could act. So if a monster has 50' movement, it could use 10' to move to an enemy and a standard to attack. It could then use it's remaining 40' of movement as it saw fit (basically this works a lot like spring attack in practice).
Increased actions: A monster with this template can perform two additional actions:
1: Healing Surge: If the monster has a fast healing or regeneration score, he can, as a standard action, heal a number of hit points equal to his constitution modifier multiplied by his fast healing/regeneration score.
Exemple: Rock the troll is trying to fight off those pesky adventurers, at the end of the turn, he has a standard action, being a solo monster. He uses the healing surge action, and has a constitution of 23 (+6), and his regeneration is 5. He heals 30 HP, and then roars at the PC's.
2: Self Aid: The monster can opt to use his standard action to either give himself +5 to the next attack roll he makes, or +5 to AC vs the next attack.
Exemple: Tuskgutter is just a simple solo boar. After having charged and gutted an adventurer, he finds himself surrounded. He decides to use a standard action to roll around in the entrails of the PC he just killed, granting himself a +5 bonus to AC vs the next attack he receives.
3)HARDER Maximize HP per die, add 3 Hp per HD. The proper equation to calculate is : (HDx#HD)+((Cons mod+3)*HD). At CR 13+the modifier is 4. At CR 20+, the modifier is 5.
Exemple: The Juvenile red Dragon has hp 149 (13d12+65) normally. You apply the solo monster rules and now his HP becomes:
(12*13)+((5+3)*13)=260 Hp. He will definitely last longer vs a group of optimised PC's
4)STRONGER
Pick one of the following as a defensive measure for your solo monster.
Tenacity (SU)
The lone wolf can spend a move action to remove any action inhibiting status (Frightened, Cowering, Stunned, Dazed, Nauseated, Dominated, Charmed) by paying a number of hit points equal to his HD. This move action can be spent even if his normal move actions cannot be used.
Immunity (SU)
The lone wolf has a barrier that protects him from action inhibiting statuses (Frightened, Cowering, Stunned, Dazed, Nauseated, Dominated, Charmed). this barrier can be taken down by a successful sunder or dispel magic attempt aimed at the barrier (DC=10+CR). This sundering attempt does not provoke attacks of opportunity. This barrier can be refreshed as a move action.
Willful (SU)
A Solo Monster has a pool of 3 Solo Points. It regains 1 SP per round just before its turn but never has more than 3 in its pool.
In between players' turns, it can spend SP, similar to coming out of Delay. It cannot spend SP directly before or after its turn; if it wants to spend SP when its turn comes up then it has to Delay its turn until at least one player has gone.
It can spend 1 SP to remove an action inhibiting status , or suppress a permanent/long-term one one (like a curse or disease) for the rest of the encounter. It can do this even if the condition normally prevents action or decision-making. It can use this to stand up from Prone without provoking AoOs.
It can spend 1 SP to cast a spell/SLA on itself without provoking, like a war priest.
It can spend 1 SP to take a standard or swift action. This also entitles it to single-speed charge and withdraw actions and 5ft steps. This also refreshes its pool of AoOs.
Tell me what you think of the mods, I've tried to put them in bold.