What late-cycle solo fixes are you referring to?
Early 4e solos had not always really figured out how to deal with the action economy yet in a solo fight.
The 4e MM solo purple worm for instance is just a big monster with a single target attack. The closest it gets to a group dynamic solo mechanic is if it spends a round to swallow a creature for no damage then it can next round bite another while doing acid to the swallowed one.
Purple Worm Level 16 Solo Soldier
Huge natural beast (blind) XP 7,000
Initiative +13 Senses Perception +10; blindsight 10, tremorsense 20
HP 780; Bloodied 390
AC 33 (26 against swallowed creatures); Fortitude 34, Reflex 30,
Will 29
Immune gaze, illusion
Saving Throws +5
Speed 6, burrow 3 (tunneling)
Action Points 2
m Bite (standard; at-will)
Reach 3; +21 vs. Reflex; 2d8 + 7 damage, plus the target is grabbed (until escape). The purple worm cannot make bite attacks while grabbing a creature, but it can use clamping jaws.
M Clamping Jaws (standard; at-will)
If a purple worm begins its turn with a target grabbed in its jaws, it makes an attack against the grabbed creature: +21 vs. Reflex; 2d8 + 7 damage. Miss: Half damage.
M Swallow (standard; at-will)
The purple worm tries to swallow a bloodied Medium or smaller creature it is grabbing: +21 vs. Fortitude; the target is swallowed. The swallowed target is inside the purple worm and is dazed and restrained until it is no longer swallowed. The swallowed target has line of sight and line of effect only to the purple worm, and no creature has line of sight or line of effect to the swallowed target. The only attacks the swallowed target can make are basic attacks. At the start of each of the purple worm’s turns, the swallowed target takes 10 damage plus 10 acid damage. When the purple worm dies, the target is no longer swallowed and can escape as a move action, appearing in the purple worm’s former space.
Alignment Unaligned Languages —
Str 24 (+15) Dex 16 (+11) Wis 14 (+10) Con 20 (+13) Int 2 (+4) Cha 4 (+5)
The later cycle 4e essentials Monster Vault Purple Worm has some more options as a solo. It can minor action stinger, triggered reaction thrash, and get an extra minor when bloodied. It interacts with more of the party during the solo fight:
Adult Purple Worm Level 14 Solo Brute
Huge natural beast (blind) XP 5,000
HP 560; Bloodied 280 Initiative +12
AC 28, Fortitude 28, Reflex 26, Will 24 Perception +11
Speed 6, burrow 6 (tunneling) Blindsight 10, tremorsense 10
Immune blinded, gaze effects
Saving Throws +5; Action Points 2
TRAITS
Ponderous
The purple worm can take immediate actions while stunned, dazed, or dominated.
Blooded Frenzy
While bloodied, the purple worm takes an extra minor action during its turn.
STANDARD ACTIONS
Bite ✦ At-Will
Attack: Melee 3 (one creature); +19 vs. AC
Hit: 4d8 + 8 damage.
Devour Whole (acid) ✦ At-Will
Attack: Melee 3 (one creature); +17 vs. Fortitude
Hit: 3d10 + 7 damage, and the target is swallowed (escape DC 21). While swallowed, the target does not occupy a square and has neither line of sight nor line of effect to anything except the worm and other creatures swallowed by the worm; in addition, nothing has line of sight or line of effect to the target except other creatures swallowed by the worm. If the target attacks the worm using a close or an area attack, that attack targets all other creatures swallowed by the worm. While swallowed, the target takes 30 acid damage at the end of its turn. When the effect ends or the worm drops to 0 hit points, the target appears in an unoccupied square of its choice adjacent to the worm.
MINOR ACTIONS
Fling ✦ At-Will
Attack: Melee 3 (one creature); +17 vs. Fortitude
Hit: 3d10 + 8 damage, and the purple worm slides the target up to 4 squares.
Poison Stinger (poison) ✦ At-Will
Attack: Melee 3 (one creature); +19 vs. AC
Hit: 2d8 damage, and ongoing 15 poison damage (save ends).
Regurgitate ✦ At-Will
Effect: One creature swallowed by the purple worm appears in a square of the worm’s choice within 4 squares of it. That creature is no longer swallowed and takes 3d10 + 8 damage.
TRIGGERED ACTIONS
Thrash ✦ At-Will
Trigger: An attack hits the purple worm.
Attack (Immediate Reaction): Melee 3 (one or two creatures); +17 vs. Reflex
Hit: 3d12 + 5 damage, and the purple worm pushes the target up to 6 squares.
Str 25 (+14) Dex 20 (+12) Wis 19 (+11) Con 20 (+12) Int 2 (+3) Cha 4 (+4)
Alignment unaligned Languages —
The Draconomicon was early in the 4e cycle so the dragons from there generally were not as developed in their solo mechanics as later cycle solos.